I suspect that the number of RP with a new partner is less than the number of NRP with a new partner as it's easier to date when you're a NRP.
I have a friend who is the RP and she is brilliant - funny, clever, caring, good looking - but she cannot get a new partner, it never works out. She'll arrange a date and her ex will drop her in the shit by saying he's "too busy" to have the DC even though it's his weekend to. Or one of the kids will get sick. Or her childcare will crap out. Or she'll start dating someone and it'll seem like it's going well but 4-5 dates down the line he'll say he's "not looking to play dad", and this is way before the point where she'd even be considering introducing them so there's no suggestion of anyone being expected to "play dad".
Her ex meanwhile has had numerous relationships in this time, including one that lasted nearly three years, has cancelled his weekend with the DC time and again because he's had a better offer (date, lads weekend away, going to watch the football, the kids have got a cold and he doesn't want to catch it - all actual excuses he's used). He's now living with a girlfriend and they're due a baby in January. She's had no maintenance off him at all for the last eight weeks because "girlfriend wanted to buy the nursery furniture" so my friend has been in the awful position of trying to stretch her income way beyond the point it is capable of stretching to and selling her belongings to make up the shortfall. He has also cancelled his last three weekends with them because "girlfriend is a bit tired so they can't sleep over because they wake up too early". I doubt the girlfriend knows she's being used as an excuse.
He isn't being honest and is spinning you the line many Men do about either the Ex taking all his money, or not letting him see the kids.
Or being unhinged, crazy, vindictive, lying etc.. There's a script.
I always think you can tell a great deal about a man based on how he talks about his exes, especially if they have children together.