It's an odd system which prevails these days. Used to be, you'd start as a lowly in-betweener as part of an animation team, move up to animator/lead animator, then perhaps second director, then finally solo director on your own short film projects, and perhaps do a big "masterpiece" (e.g. a feature film) before you retire... or even several. That used to be the career path in Soviet animation.

But now, they start out directing their own films as students (first ~2.5 minutes, then 5+ minutes), perhaps make one or two more longer ones, and then if they're lucky they get hired to work as in-betweeners on some big producer-driven series or feature (as often as not directed by some random first-time director). So - the higher you rise, the LESS creative control you get. Aside from a very few exceptions.

As a career arc, it seems a lot less inspiring...

Also, it means that perhaps most animated shorts are actually being made by students.