Isn't it the same with manga artists? Why do they even work in these jobs then?
For manga artists, I don't know.
For the second part of your question, these last years, many animators of the Japanese animation world (whether they are high or not hierarchically in the studio or even independent) leave more and more in the Game Design, therefore in the development studios of video games (to quote only the most known in Japan: Square Enix and Capcom).
Because of the lamentable working conditions they undergo.
God that's a sweatshop! They're treated like slaves!
To repeat what I said above, a Japanese studio pays its animators a fixed salary of 500/600$ per month. The animator in question earned 1 000/1200$ with the 300 drawings made per month.
The fixed salary depends on each studio.
And finally, it is the Japanese society that is like that. In Japan, the more you work (including overtime), the better you are perceived. That's the way it is, and always has been.