You're absolutely right that there are a lot of "invisible" devs, both new and veterans, that people are never aware of. As a 10 year vet I doubt anyone would notice if I left as I do not have any sort of real presence on social media. Likewise, most people don't even know I, and the multitude of other vets, still exist. Similarly, my sister got hired as a designer a few months ago and there was no hoo-ha about her arriving for the same reason.
The game industry is a constantly shifting place, no matter what company. There will always be people who want to move on for personal reasons, and people who want to stay in one place for eternity. Doesn't make one better or worse than the other; it's just how people are.
So the moral of the story is: do not look at a single publicly visible artist being hired as some sort of pattern or proof of a lack of anything.
Also, a big, warm welcome to Jenn! :D
my sister got hired as a designer
wave