In my experience, a lot of single mom's once they have been in the dating market for some time and have had enough experiences to figure things out, only want a guy to be "part of her family" as a partner, dad, etc. after he ticks all the boxes and that he wants to be part of her family unit by demonstrating seriousness, commitment, stability(both mental and financial), longevity, and the fatherly and family oriented traits that a woman is looking for.
A lot of woman do not come across this exact combo for various reasons. It is the reason why a lot of them will put their kids first and only want a guy to fill the lonely gap here and there to keep them sane and to seek someone they can experience adult time with since she's with her kids the rest of the time. A lot of them only want a plate or part-time semi-serious guy to fill the void in their lives while their kids are young.
Of course there may be the rare situations where the woman feels like she's found that perfect guy that ticks all the boxes but in this day and age, I find that to be on the rare side. It's pretty much going to be her and her kids vs. you. Two separate teams.
Also a lot of these women, due to the level of male thirst and desperation along with massive amounts of simping, do not look in the mirror themselves and asks themselves how they can improve by being a classy woman and a great partner for a guy. Then it becomes one sided with her always wanting things on her terms and her always taking and taking. This kind of behavior eventually leads to her being pumped and dumped several times. And rather looking at herself as the possible cause, she gets bitter and jaded and blames all the guys. Then many just give up and think no guys can be worthy of becoming one team. Then the viscious cycle of repeats over and over...
A lot of women don't realize that treating a guy great will have him sticking around, rather they think the guy has to treat them great to stick around. That is where things fall apart IMO.