Things are often they way they are because it works on a macro and micro level. Sure, some things get into weird feedback loops and drift to silliness, but for the most part, if you see something working for a lot of people, they're not doing it just because of tradition.

The OP is absolutely correct in that many people will find it better to specialise in child-rearing and income-generation for a two-parent family. That doesn't mean one doesn't do child rearing and the other never works, but the primary responsibilities will fall down that way.

That's how it has been for a millennia or three, and that's likely how it will stay. Behaviours like this are all about reproductive success so that's why they the way they are.