I'm in utter disbelief that there's confusion over how these 'situationships' occur amongst women. It's patently obvious: men with a lot of options who are seeing women who are beneath them aren't invested in them. This could either be serial monogamy or just outright soft harems. In either case, the man has power and the women he's seeing aren't attractive enough in terms of looks nad personality for him to commit (if he even wants to commit in the first place). Personally i know a guy who didn't keep a harem, but he was pretty attractive and had a good job. Probably the only reason why he didn't have a harem was because his job was stressful so he only had time for one chick at a time. If you saw the girls he dated, they were clearly beneath him, but his relationships maybe lasted a few months to less than a year. When he finally did get married in his mid-30's, he married an incredibly attractive and feminine woman who was on his level. I'm sure he was quite happy to play the field before he finally got sick of it and settled down with an absolute dime of a woman.

The relationship zones chart below... you only need to watch first 1/5th of the video, it basically describes how attraction works for men (the first part of the video), which is quite simple and how attraction works for women (most of the rest of the video, which is going to be more complicated... because women's attraction triggers is just more complicated, deal with it):

https://youtu.be/lL13EeEhgag

The author of the video (timestamp link below) describes a situation where when he was a lowly uber driver a girl he was talking to was complaining about being in a 'situationship' with a guy who had multiple girls he was seeing and asking how she could get him to commit, he flips the script on her and ask her if he (the lowly uber driver) gave her 100% commitment whether or not she would trade the guy she was seeing for him... she would not (duh):

https://youtu.be/lL13EeEhgag?t=1159

TLDR:

Men put women in 3 zones: Keepers (self explanatory), Sleepers (eh, i find you kinda attractive, but i'm really shaky on you long term), and Sweepers (i'd be embarrassed if anyone found out i slept with you, let alone be seen with you in public on a date or whatever, so like... fat chicks or tatted up strippers with shitty piercings and a single mom of multiple kids and a drug habit). The criteria are looks (plus), personality (plus), how much time you spend with other men (minus) and other (soft plus or minus, but not really important).

FWIW, it tracks with my life, i'm about a 6 or a 7 and i wifed up my woman who's like an 8 in looks and a 10 in personality. There's no way in hell i would ever in a million years do better than i could, so she's a hard keeper for me. Hell, before i wifed her up, i might've been a 4 at best (this was when i was somewhat overweight) and got a lot of stares from people when they saw me with her, so i was highly motivated. If her personality was the opposite of what it was or she was like a 5 in looks, she... wouldn't be my wife and might be a temporary thing at best.

This is not hard and you people are overcomplicating it

If you have the time for it, there's a version 3 of the relationship zones map that's super detailed, but probably not necessary for this particular discussion:

https://www.youtube.com/watch?v=n4aMiAesXjE