@Topgub
It seems that you have been in the lucky position of being able to share childcare with your DP without outside assistance? And that both you and DP work full time?
I do know one couple like this in real life. They are both nurses and each works something like three 12 hour shifts a week. So it's hard, but it works.
Most people are not in that position. The standard working week is 9 -5 Mon to Fri. Many people work longer hours than this,
plus there's added commuting time. So most people are simply unable to do what you do, and have to make different choices to you. Sourcing outside help, or one partner becoming a sahp or working part-time for a while are the more usual options. And yes, it's mostly sahms rather than sahds...partly for biological and probably partly for cultural or traditional reasons.
You have said you believe that sahms don't even want their partners to share in childcare! I am curious why you think this? Because I think you're wrong and that women very much value a close father-child relationship and men's role in childcare. But people must make pragmatic choices about division of labour. At the moment society is not generally set up to allow two parthers to share the load following your model. Paternity leave is very poor. Usually it is financially risky for both partners to go part-time - as it is, many jobs don't allow it anyway.
Yours may well be a great set-up but it's not close to being achievable for most people right now. Please understand that many people are making the best choice they can for their family, constrained by the choices that are actually available to them. Society is not where we would like it to be and wishing that it were won't change it overnight. This is not the fault of sahps, who, like woh parents, are mostly just doing the best they can.