Children will go through a phase of identifying with each gender, they will switch back and forth, first getting close to Daddy and wanting to be like him, then Mommy, and so forth, while they learn about traditional gender roles. If they only have a Mommy, they may have a hard time learning how to be male. Also, some parents may mistake a normal part of development, (that of identifying with the opposite sex), as a permanent desire to be a member of the opposite sex. They will then encourage and push their child to stay in this role. There is nothing wrong with saying “you are a boy and boys do this, not that.”
Some women are *ag hags. There can be pressure on a boy to be more girly. Or it may come through child abuse (that was what Rip Taylor says happened to him).
Also recently overheard some women gathering at a coffeshop. They were having a meet and greet for lesbians "speed dating" it seems. Some of them even had teenaged kids of their own (not present). Some of the women were discussing how they were hoping their daughters would go bi/lesbian at least in their teenaged years to avoid pregnancy.
Mothers CAN bring their kids up wrong for selfish and negligent reasons.