Don't you think trainers that train higher potential players will try to force their main skills first (to make them interesting for national teams) and the work on the sideskills, while allstar potential trainers might round their players better, to keep their salary lower and to make sure they don't hit the cap that fast so that they can't train the sideskills anymore?
*Breath*
this isn't dumb, but especially for centers sideskills have pretty low effect on the team succes ;) But also you could handly the cap on many other ways, because training sideskills ain't that effective too, maybe the training is still fast(height *ohoh*), but they are effect on the game is also lower else they won't be sideskills.