I'm genuinely curious as to what the key differences are (especially those that would cause someone to switch), as someone who is pretty tech savvy but whose use of Linux as a daily driver is admittedly pretty weak.

You usually try a few distros, until you find the one that does whenever you needed, and then you stick with it for 15 years ;)

From my own experience: 15 years ago, when (except for academia), Linux was very nisje, it was hard to use it. Random rare errors would pop up. On Windows you would know someone who knew what to do, but with Linux? So I chose Ubuntu, because it had the most support. Solution to any error could be found on askubuntu (?) forums. But if you had a friend, you would choose his system and get help from him. I once had university admins very happy to help me with something and even give me some tips.

Nowadays it really doesn't matter that much, other than extra easy (with an LLM everything is already easy) installation of drivers (POP os?)/initial programs you used on Windows (on Mate it takes 10min due to a special GUI appstore).

BUT there are reasons to switch. Like Ubuntu's pushing of very annoying snaps, making it very hard to get Firefox without a snap. Snaps are annoying, because they don't have a cleaning mechanism and old versions just clog your hard drive. They take forever to launch and it's just not a good idea for a browser. Don't mind snaps for other things. There is also Desktop Environment support and support for hidpi monitors and such.

Other than that, there is a little of philosophy. Like super FOSS and idealistic like Debian (i guess? Pls correct me if I'm wrong). Or more business aligned, like Redhat/Fedora. Or elitist that like to waste their users time and make them read manuals for fdisk like Arch, where you have to format your hard drive without GParted or any other GUI.

I'm no pro, but that's a little that came to mind if you wanted to know what mattered in the past.

not OP, but for some it might be availability of latest versions packages (say, you've heard about new major version of Bash or Vim being released today, and wondering how soon it might be available in your distro packages), and, as someone else mentioned, less update stress due to lack of "major version bumps" - just remember to subscribe to https://archlinux.org/news/ and watch out for entries requiring "manual intervention".

I would say EndeavourOS is the "Ubuntu" to "Arch" if you will. The installer is easy, and it comes with "yay" out of the box which is a frontend to Pacman which holds your hand in just the right ways. If I want to update my OS I type "yay" into a terminal, hit enter and confirm the packages needing updating (or select which ones I want) and type my password, and that's it. In the past with Manjaro I did a system update with Pacman, and problems ensued.