For me I find PPAs typically make getting the latest versions of software where I want the bleeding edge painless. And I don't need to also have everything bleeding edge the way Arch forces me to.
The last time I seriously tried to use Ubuntu was probably 8-10 years ago and I ran into a lot of trouble trying to get up to date graphics drivers via PPAs. I also remember being tired of having to go find a random PPA for every piece of software I wanted. Most of the time I would just find some random blog that provided a "PPA for up-to-date package X" and ultimately felt like what I was doing wasn't really any better than downloading random MSIs like you would on Windows.
With Arch though you get the AUR which quite literally has every piece of software you could ever want and is at least managed and maintained in a central place so you're not just adding random PPAs for everything.
I don't think the AUR is necessarily more secure but in general the nature of how the AUR works does perhaps give some slight advantage. The suggested approach to the AUR is to download and inspect the PKGBUILD so you know how/what the package is doing opposed to a PPA typically being a precompiled binary. AUR helpers will also typically show recent comments, etc. so if a package was compromised or had issues you'd probably know as you're pulling it down.
Really though the AUR just tends to be more convenient and complete than finding random PPAs in my experience.