As far as I can tell, this is the only reason, you'll likely lose a bunch of functionality (that's been my experience); so "principle" is the only reason I'm aware of (or minimalism, but that's a principle too is it not?).
I suppose if nothing else, you can run a more up to date firmware if the vendor stopped supporting yours, but I have no idea what that means in a practical sense.
As far as I can tell, this is the only reason, you'll likely lose a bunch of functionality (that's been my experience); so "principle" is the only reason I'm aware of (or minimalism, but that's a principle too is it not?).
I suppose if nothing else, you can run a more up to date firmware if the vendor stopped supporting yours, but I have no idea what that means in a practical sense.