Child of really toxic father here. I can honestly say that the amount of time that I was made to spend with him as a child did lots of harm to my mental health.
My father never paid maintenance either and (no surprise here) did nothing with me when I was with him. I was ignored, given bags of sweets and other rubbish to keep me quiet, foisted off on to other relatives and a string of girlfriends.
I think you’ll find a strong correlation between men who won’t pay for their kids and men who really don’t care about their kids. Why would you not want to pay for your kids to be warm and fed or to go to nursery if you really loved them?
These men want to have their kids around to pretend to be a great parent or to just avoid paying maintenance. It’s also a great means of controlling their ex partners, to ensure they can’t live happily without worrying about how to pay for everything and living with the stress that poverty/debt causes.
Those posters who think that they know enough to tell the OP off about her attitude to a man who changed his hours to part time so that he didn’t have to pay maintenance should have a rethink. Refusing to pay anything for your child is abusive to your ex partner and child. Frankly, the less time any child has to spend with an such abusive man the better.
A good parent understands that they have to provide for their child, both financially and emotionally. That involves investing time and money, often putting yourself second to their needs.
If you can’t put your child’s needs first, then you really shouldn’t be allowed to spend a great deal of time with them and they are better off with the parent who is prepared to put the work in.