Nope, not all prenups have to do with money and trust. Lookup legal and medical proxy prenups, usually keeps the state out of personal affairs if a partner becomes incapacitated or dies. Funds don’t go into a suspended state because of the prenup if partner doesn’t have a will or an estate plan.
Then doesn’t a lack of a prenup show a lack of trustworthiness? That seems even worse. You’re still preparing for it to go wrong. Except then you’re planning FOR it to go wrong. The only rational reason not to do a prenup is that you want to profit from it as much as you can “if” it does. And if that’s your attitude going in, then it almost certainly will