Why do coparents date expecting the next lover to be different and not give them another kid to take care of?

See this so much and it's so dumb how all their friends usually warn them about this new lover and get the result is always the same?

One parent taking care of one or two kids ends up with another?

It's not just girls any more it's often single dads too.

Like there is ways to prevent this and there are many ways to prevent this! Not just a rain coat

Why do coparents date expecting the next lover to be different and not give them another kid to take care of?
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