Why are you surprised? Middle-to-low income men are not represented by any powerful lobby or movement (because that would be branded misogynistic and/or racist).
Want more surprises? Compare what US companies are allowed to put into food to their EU counterparts.
Lots of things that would be (and are!) labeled misogynistic and/or racist are represented by powerful lobbies and movements, so the logic there doesn't follow. It may be that middle-to-low income men are not represented by any powerful lobby or movement, but if so, the reason you offer is not the reason why.
(The reason why is probably that middle-to-low income men don't, as a class, necessarily have lots of free money to devote to political causes, and, to extent that people in that class do devote money to such causes, they don't do so around their identity as "middle-to-low income men".)
I see class and sex. What exactly is the race angle?
Single mothers are a growing group, they now represent 1 in 4 households. They are a very important group to win elections. For example, single mothers were the single largest voting bloc for Obama. A lot of campaign strategies are designed around winning the single mother votes, "the war on women" rhetoric for example. It's not surprising to see laws designed to coddle them and cater to them.
As this article points out, this is very shortsighted since for one single mother who gets "free child support" it's a whole family who has to suffer, but people are slow to make the connection.