I think you’ve got some misconceptions about open marriage/polyamory. My point is not that women are wanting other partners and leaving men at home by themselves -it’s that they are the first ones to bring up the subject.
Polyamory means that both/all parties are free to seek other intimate relationships and that is how it usually goes unless one person has decided that they don’t wish to have other partners. If they want them, believe me, there are plenty of partners for men in open marriages. It is not a lopsided dynamic or inherently callous dynamic at all.
You are also operating under the misconception that open marriage is always primarily about sex. In the case of swinging, that’s probably true, but not necessarily so for polyamory. Sex is typically a part of the equation but is not the only aspect. I have another partner whom I don’t see (or have sex with) anymore because he now lives far away from us, but I still have a strong emotional connection and relationship with him.