Erm, maybe because you have kids and this is what happens
Gosh I must have missed that time machine that transported us all back to the 50s. How could that have happened? 
Men manage to find women happy to be sahm's why can't women do likewise.
I don’t even know where to start with this one. Honestly.
But firstly, the numbers of SAHD are minute when compared to SAHMs. We could have an interesting debate around whether that’s for societal, cultural, biological, industrial reasons, but that’s the fact. So you’re asking the impossible as a start off.
Secondly, increasing numbers of SAHDs, while laudable in some senses, would just put men in the same vulnerable position as women can be in now (no income of their own, lack of pension contribution, skill gaps when trying to enter the workforce, etc.)
As a solution to solve the problem it’s just total nonsense and I’m sure you know it