I'm only 6 months into the 'linux world', I don't understand what Ubuntu's competitive advantage is. I only used Debian and Ubuntu (and Parrot OS) and I don't see anything missing in the former (that can't be added manually)
That user base didn't make them any money, plus a bunch of derivative distros showed up to compete with them for it. So these days they've pivoted to a server focus and it's still an OK desktop distro with one of the largest user bases, but it's not head and shoulders above the competition like it was 10 years ago.
Personally I've been running Ubuntu on the desktop for over a decade myself, but the main reason I haven't moved to Mint is... emmhh.... I have better things to do than reinstall my OS? Next time I need to do it, that may be all she wrote for Ubuntu
Now though? The rest caught up. Even in the last five years things have become incredibly painless across most desktops and environments. Ubuntu still has the big (for Linux) brand recognition, but on the desktop isn't anything special anymore, and if anything has begun alienating its users with forced snap packages, Amazon bloatware (although I think that was removed finally) and forced system upgrades.
As always, people have forgotten just how much of an improvement Ubuntu was on other distros in stability, UI and feature set.
I switched back to Debian (12/bookworm) a few months ago because of Ubuntu's snap packages. I've not noticed any downside yet.
More up to date then Debian Stable. You can use backports, sid, or testing and be more up to date than Ubuntu.
I still probably wouldn’t run it in prod, but for desktop? Without a question.
My experience is don't run Canonical-developed (as in it originated from Canonical) software, it almost always breaks, get dropped, or they decide to screw around with the licensing. I think early on they tried to copy Fedora (e.g. having the latest by pulling from Debian unstable, 6-month releases), but now they're trying for the enterprise (and trying to copy RHEL), but they lack Red Hat's culture to pull it off.
2. Most proprietary software offer Ubuntu/Debian and RedHat/CentOS packages and support.
3. LTS versions , some people do not like or need latest software version with latest features and the new bugs
4. Ubuntu pays developers that work directly on Debian and some devs were(maybe still) struggle to fix Gnome bugs that Gnome ignores
And shipping ZFS
Debian was notoriously out of date. Debian Stable mostly contained packages that were several years out of date, and even Debian Testing often didn't have e.g. recent drivers and browser versions in its repo. Debian Unstable, on the other hand, was too unstable due to being rolling release. My subjective experience was that things like getting MP3 codecs to work or nVidia drivers installed was also a huge hassle. Ubuntu was based on Debian, but ensured that the latest versions of all these things either just worked, or could be easily enabled.
Secondly, I remember Debian as being largely a "do it yourself" option, not so different from what an Arch user today might be after. You used a curses-based installer, selected what packages to install manually, customized everything from the terminal, and so on. Ubuntu offered a cohesive desktop experience - it gave you a pre-configured Gnome desktop with all apps and drivers an everyday user might need, and slapped on a (subjectively) aesthetic and coherent theme. The installer itself was also a friendly GUI that even non-techie friends could use. If you wanted to install it, you didn't even need to know how to flash an ISO, you just put your address on the Ubuntu website and they literally mailed you a CD containing the installer - and nearly anyone could install Linux using it.
I think "peak Ubuntu" was around 2012, after that they became too large and things started going downhill. They split the Gnome user base by creating Unity instead of contributing to Gnome Shell, they split the post-X11 development by pushing Mir instead of contributing to Wayland (I think related to the failed "Ubuntu Phone"), they added Amazon ads (with privacy concerns) in the default desktop experience, then they started pushing Snaps, etc. It's been largely downhill since then, but they had already become the "default Linux distribution" targeted by companies like e.g. Steam, so they kept chugging along.
Personally, I still think Ubuntu works quite well if you want something Debian-like that is release-based (not rolling release) but updated more frequently. But I in that case prefer using Ubuntu Server edition and installing my own packages via apt, that way you get all the Ubuntu compatibility of running a mainstream distro, but you avoid most of the clutter in the default distribution. There's many forks like PopOS and Mint that can be used instead though if you want something that continues in the original spirit of Ubuntu.
From what I've read, Ubuntu was easier to install in the past but today (at least with Debian 12 Bookworm) Debian is just as easy to install and use imo. I've actually had less problems with Debian compared to when I was using Ubuntu.
All the other distros have caught up so there is less to sell Ubuntu on, but it was one of the first. They also had their 1000 paper cuts project where they spent a lot of time fixing everyone else's bugs and submitting PRs.
Historically, Linux has always had more distros than the open source community (and the closed-source-but-targeting-linux community I guess) can support to a high standard.
This has meant there is always one leading distro, which everyone packages for and documents for and guides newbie users towards. For a long time this was Red Hat Linux; they decided not to do that any more right about the time Ubuntu came out.
Ubuntu has held onto that position up to this day.
I see what you did there
I used Debian for several years before moving to Ubuntu. The reasons for that move are twofold: First, I bought an Nvidia graphics card. Second, Ubuntu has newer packages. Sometimes I need a very recent release of something, and Ubuntu is far more likely to have that. I also like Snap as a failover from apt: the only time I use snap is when I run into a situation like this:
> shit, this package is broken and there's about 200 steps I'd need to adapt from ArchWiki to fix it. You know what? I'll just snap it.
I am strongly considering going back to Debian, though. I run a kinda weird setup on my personal machines (I start with Ubuntu Server, then hand-install graphics drivers, xorg, i3wm, st, etc etc) and a lot of Snap packages seem to assume I'm using GNOME even though I'm not.