A couple of women have asked me this as a guy and I honestly I don't really know how to answer them. I mean yes I'm a guy who has been noticing much better patterns with women and men than I can say for most people my age but at the same time I never feel I can confidently answer this one. Not in a sense I'm not so sure at all why this happens but if I'm being mostly on point with my answers.

Of course if you had to ask me flat out and I felt confident enough to give an answer not relating to the obvious (xyz girl over here provides the value that said guy needed in his time of life) it can summed up to men putting in alot more investment into said girl that he wants commitment from. Mostly that can be from chasing or how long they knew each other.

But this is where Reddit comes in. Let's say a guy is having sex with a girl and they have been together in a non committal relationship for a while now. Then all of a sudden the guy gets into a relationship with a totally different girl.

What gives? Is it usually the investment he put into Girl A over Girl B?

Edit: I just came up with an obvious realization after reading the comments. Now I'm not dead set on this belief I could be wrong on this.

But it can be as simple as guys knowing who to pull this with and who not to. Take for example. If a guy who's 6ft 5 shoves a guys who's 5ft7. There's a decent amount of odds in his favor that the guys whos 5ft7 won't respond. Because he's smaller.

So apply that to dating. The girls he knows won't stick around for casual relationship he has to lock down.