The patriarchy is a system. It benefits men, but men aren’t the only participants. It’s not a cop out or an excuse. It’s the system we live in, and it’s embedded in our society.

You seem to forget that all these men still possess personal agency in relationships. They can set boundaries and protect their friendships. In the cases I know where women have been against female friends, it’s because the man has been a cheater or otherwise inappropriate in his relationships with other women. That happens, too. But I don’t know of any healthy couples where one partner isn’t allowed to have friends. Your experience isn’t the norm and doesn’t describe healthy relationships. Either your friends are serial cheaters or they’re in unhealthy relationships and unwilling to set boundaries with their partners.