one-penis-policy in straight male / bi female couples, why is this such a common structure

genuine question not trying to start a war. been lurking and going to clubs for about 2 yrs, we're a het couple (F33 M36, bi-curious tipping bi for me, hes straight). and the more meets we go to the more i notice this pattern, like an absurd amount of couples we cross are running OPP. she plays with women, she plays with couples, but her playing with another man solo is off the table. meanwhile he can do whatever he wants. this is sold as "what works for us" by basically every couple we've asked. and look. im not saying its automatically gross. but the asymmetry is wild and its always the same direction?? ive literally never met a couple running "one-vagina-policy" where she can play freely with other women but he cant play with another woman without her. ever. its always the man's genitals that need protecting. so i wanna actually understand. is it insecurity dressed up as policy, or a genuine preference she also wants (and if so where does it come from), or maybe a remnant of bi-women being more accepted than bi-men in the LS, or something about competition between men specifically, or something else im missing entirely. we're not running OPP and don't want to but i wanna stop being weird about meeting couples who do. like i wanna actually get it from inside. ppl who run OPP and feel good about it, talk to me. ppl who used to and stopped, also talk to me.