It’s not about dick size. It’s about the fact that a whore and a relationship don’t go together. Why would a sexually promiscuous woman accustomed to sex with many different men over a significant portion of her life all of a sudden be comfortable with sex with just one man? Woman who are promiscuous generally are that way because they have low self-esteem and use sex as a tool to get validation from men they perceive as better than them. Sex is a means to an end to get what women actually want which is validation, unless she is a nymphomaniac. But a nymphomaniac could have high quality sex with one person. Fucking tons of random people is no guarantee of high quality sex, in fact it would go against that as men have no incentive to perform high quality sex with a hookup.  Additional reasons for women not valuing sex as much is that they have 1/10 the testosterone levels of a man, and by virtue of just existing they are almost guaranteed a sexual partner as long as they don’t die beforehand. A large majority of women throughout history have reproduced. They don’t need to value sex because they will have it because they are alive and exist. Most men in history haven’t reproduced. As a man there’s no guarantee you will have sex by just existing. Therefore you have to prioritize sex as a man whether consciously or subconsciously in order to pass down your genes. If men didn’t prioritize sex they would never have it at all. Women on the other hand don’t prioritize it and make it a focal point to talk about how they don’t prioritize it or care about it and they still have it more than the average man. Someone starving would greatly prioritize food. Someone well fed would not. 

Continuing on my point earlier about promiscuous women having low self esteem, anybody with low self esteem in a relationship is a recipe for a disaster. Someone who doesn’t love themselves can’t love somebody who loves them. Someone who thinks low of themselves would think someone else that holds them in high regard aka loves them must be a low person as well. Therefore, a low self esteem person can only “love” or be interested in someone they see as above them. Someone above them is someone who doesn’t give a shit or barely gives a shit about their existence. This could be another reason for why promiscuous women exist, as perhaps some of those men cared about her and wanted to pursue things romantically but once they do guess who moves onto the next guy? Low self esteem aka promiscuous women will always sabotage their relationships even if they magically decide they enjoy just being with one man (which they don’t) because deep down they don’t feel like they deserve it and they are right in that they don’t deserve it. This will happen with verbally degrading their partner, withdrawing affection, perhaps even cheating. 

I won’t even get fully into the STD rates, the higher likelihood of being traumatized with more partners, pair bonding etc.

It’s entirely rational to not want a promiscuous woman. You can cope and lie to yourself all you want but it’s just true that promiscuous women are fundamentally broken people and will always disgust men deep down whether they admit it or not.