Only single men get upset at this.
It's because it messes up the market.
Think about it like this.
When a professional basketball or football team gives a player an insane max contract, other teams get upset. Not because they don't like or care for the player that got the money, but it's because that contract has the potential to affect future contracts. If Player A just got $200M guaranteed, then Player B will want $250M guaranteed, especially if B thinks they are better than A. Those kinds of contracts can destroy teams. Teams who already have their stars under long term deals don't really care.
So brehs wifing up single moms potentially disrupts the market, because more and more single moms will be popping up demanding max contracts. Brehs in committed relationships/married don't really care.