What is it???? ???
Simple economics?
There is an ample supply of women without kids, plenty of alternatives to single moms.
The ultimate benefit (true love, companionship, relationship, bonding, etc., whatever) is the same whether it's a woman with a kid or without.
At the beginning of dating, a single mother is just as much a stranger as the single childless kid. Equal potential.
There is greater inherent risk in dating a single mother.
Hurt her, you hurt her kid too.
There are greater costs (opportunity) with dating a single mother.
Logistics are more difficult. Learning to communicate takes longer.
Separating and seeing the woman as an individual, thereby getting to know her and her consistent behavior as a whole person, rather than as an extension of her kid(s), takes longer.
The longer communication takes = higher potential for miscommunication = higher risk of failure along the way.
If I were to say to you "I'll give you 1 million dollars, but you have to choose 1 of 2 tests. 1 is to go find a store that sells hoops, then jump through 4 hoops for 3 months, the other test is to go online to amazon and immediately buy hoops, then jump through 4 hoops set on fire, where one misstep also sets these kids on fire, and you have to do it for 2 years," which would you choose, which would be the more attractive option?
What would you say if, while you're trying to jump through the non firey hoops, the president of the Firey Hoop Child Immolation company kept calling you a coward for not buying and jumping through their hoops?