1) You are pedestalizing the girl. Most of the time, the girl is on or near the same league as the guy and you are just wearing your pvssy goggles because you are beta af or jealous that you aren't getting laid right now. Men also have a bad habit of assuming any girl that puts up a normal appearance in public is normal and an angel when she can more than likely be some mentally crazy hoe with a pot problem.
2) The Post glow up.. Maybe they have been dating for a while and during the process the guy let himself go and doesn't look like the Mike she was initially attracted to. In addition, she cannot just leave the relationship due to an assortment of reasons. You see this couple and it looks like this bloated bum of a man got in to a relationship with this gorgeous woman, but in actually this guy used to be way better looking and let himself go.
3) Simp Betabuxing- This woman has so many skeletons/baggage that the only man that will commit to her is a beta male simp. This girl could have 3 kids from a dude in jail. This woman could have mental health issues. I could go on, but just like 1) you only see a beta male with a hot girl, so you completely disregard the situation.
4) Dating down for security and power- This woman prefers to have a man she can command and mentally dominate over a good looking Chad that will do the **** whatever he wants and treat her as a second option
5) First BF- This girl met this man before she realized her full potential
6) Extreme Physical Preferences- This also applies to men(black men cough cough) but some women value race to a point that they are willing to date down in looks to be with a certain race. I used to see this with asian women and white men, but I' see it 99% of the time with black women and white men. In addition, a woman might date down if the guy is tall, skinny, beard, dad bod,baby faced, or etc.
7) Moneyyyyyy- pretty self explanatory because this is the most notable one