Maybe they never wanted the child in the first place?
Lets face it, contraception is mostly geared towards women, men actually only get 1 option (excluding the permanent operation of a vasectomy) the condom. A lot of men find them uncomfortable, that they drastically reduce feeling, and so really dislike them. That is a valid way to feel, but women tear them to pieces for it. Women on the other hand, get so many more choices. Pill, patch, shot, implant, IUD, copper IUD, sponge, cap, female condom. Possibly others i've forgotten. Yes, many of them are hormonal, BUT there are more than 1 none hormonal option, and even the hormonal ones, the pill especially, there are so many different formulations theres usually one that suits a woman if you persevere to trying them out. If a woman states she hates the pill, or doesn't want an IUD etc, it is considered HER body, HER choice, it's totally acceptable for her to refuse any and all female contraceptive methods because she doesn't like them, and insist on the male condom, but if a man does the same with his only option (the condom) and wants the woman to use a female contraceptive, hes the bad guy?
And 98% effective is with perfect use, condoms are rarely used that way so the actual failure rate is much higher.
If an accidental pregnancy happens, then its out of the males hands and 100% up to the female whether or not to progress a pregnancy. You can literally force a man to be a father when he never wanted to be, and to expect him to pay for the privilege, is wrong imo. If you know a man doesn't want a kid and you choose not to abort, you should take on 100% of the financial responsibility.
Even planned pregnancy, people can realise afterwards it was a mistake and a child isn't what they expected and is no longer what they want. Unfortunately it's not like you can give up a child like you can a pet, its a commitment you cannot go back on, and in some cases, this leads to the person trying to distance themselves as much as possible.
Their standard bills are also possibly higher once they move out as they arent being split between 2. They have full responsibility for all bills, and lets face it nobody wants to just exist, making just enough to cover outgoings with nothing left over for fun or leisure. CMS don't take bills in to account, they just go off a percentage of wages, and it can leave the NRP with nothing extra, or unable to cover all their other bills since it is deducted first.
Some may have the mentality of they aren't with the child so why is it their responsibility, or begrudge you get benefits etc, or even just hate the mother enough to want to punish them.
As for women who actively support their partner paying bare minimum, does anyone ever really want the baggage of kids from a previous relationship? Some will take it on because they love the man, but they will surely dislike money from their household going to some other woman for the kids, taking away from their own disposable income, or meaning she has to pay a higher percentage of the bills instead of 50-50 as he can't afford it after maintenance. Shes bound to want her life as minimally financially impacted as possible, especially if she is wanting/has her own children.
Kids just arent everyones top priority or want in life.