The people on VF3 progress very slowly in their careers. Compared to VF2 and 1, where they'd reach level 6-8 easily, I've noticed my peeps rarely make it to level 4 even with all the upgrades. To get to max level you'd have to upgrade their career progress with coins.
The devs want to make it hard to earn coins because they want people to pay $$$ for them. Makes sense, but everything's so expensive