Why stop at GNU/Linux? Why not Firefox/GNOME/X11/GNU/Linux?
The GNU project started in 1983 with the explicit intent to replace proprietary components of an operating system in order to build a completely free operating system. Can you tell me any other project in the 80s that did that? Of those were any even half as successful as the GNU project? Or still relevant today?
Misunderstanding GNU as a collection of little tools doesn't get you far; the C library, the complete compiler toolchain (binutils + linker + compiler), Unix userspace libraries and shells, etc --- all that got us very close to a completely free operating system in the late 80s / early 90s. Linux arrived in 1991 and in short order we had a free operating system --- with no small thanks to GNU.
The project was so successful that the scope of what makes an operating system kept growing, while people took the foundations for granted. These early achievements stand on their own.
- Linux exists and the expected benefits of the Hurd (e.g. more fine grain virtualization, userspace drivers, etc) aren't enough to mass-motivate people to switch to contribute to the Hurd.
- Commercial support. Getting your contributions into Linux is cool, because you can tell employers that your code runs on millions of computers. Nobody cares that you contribute to the Hurd.
- the most usable distribution of the Hurd is closely tied to Debian, for historic reasons and due to the fact that the most senior developer is a Debian maintainer. This is an obstacle to me, because it means that you can't just take the code from the Hurd repos and build your system. You need to use Debian patches and it's confusing to figure out what code is actually used.
- the famous Critique of the Hurd by former contributors was devastating to morale as it suggested big changes to overcome some denial of service problems. More people explored whether other microkernels could be used and a lot of time was wasted for no perceptible gain. GNU Mach is just fine for the job.
- the Hurd doesn't make use of recent hardware features. That's because of the above issues. Although slow progress is made by a handful of volunteers, there's no 64bit version, no SMP, no booting on ARM, memory / storage limits, etc. Nothing insurmountable.
- no project management. The GNU project is not a "project" and RMS is not a leader. There's neither funding for the Hurd nor is there any form of support from the "GNU project".
Having said all that, there have been exciting developments in recent years. The increasing use of the NetBSD rumpkernel for userspace drivers such as audio and disks (much more recent than the old Linux drivers and ironically more compatible license-wise), Guix System on top of the Hurd, etc. Many Debian-only patches are slowly being accepted in the different upstreams (glibc, libpciaccess, etc) and the project has become easier to contribute to.
Still, the biggest problem is the lack of self-motivated contributors. There are people that think it would be exciting to contribute to the Hurd, but then they end up requiring hand-holding from one of the very few active contributors, so eventually nothing gets accomplished.
Your platform isn't your optional dependencies.