I haven't completely stopped, but I was able to change enough to stop making them bleed and hurt.

There were a couple factors for me. First, I started to recognize that I'm some form of neurodivergent and biting my nails was a stimming behavior for me. Sometimes it was stress related but if you look up stimming behaviors there are a number of other things that can trigger it.

I made a conscious effort to replace biting with something else. In my case I found I was still putting my fingers to my mouth subconsciously so I switched from biting to using my teeth to scrape under my nails. It sounds gross, but my nails are always so short that there is nothing under there. I still don't catch myself sometimes and bite them, but I catch it often enough that my nails are super short, but not painful and bleeding.