I just dont understand why they'll make mvp spendable on mounts or minions.

It should be like a reputation system, And players with higher mvp should have queue priority. That way players will have to be nice / considerate / helpful.

Some players dont care about minions and mounts. And what if a player gets all of these items and dont care anymore about mvp?

I just dont think purchasing certain items with your reputation is the way to go.