It's completely arbitrary but with suggested guidelines.
Ah, some things never change I guess. So, given it's Inno, odds that the limits are actually one of the following:
1) Actual time guidelines.
2) Crowns spent overall
3) Crowns spent on gwen wheels
4) How annoying the world is to moderate, both in game and on the forums
5) All of the above
I know you can't answer Tokano, this is more of an open question to everyone else