I think these deadbeats seek to exact revenge on their exes by not paying support of course the children get the worst of it. Sure can't have much love in his heart if he's willing to give up visitation for a few bucks, with a PhD he should be able to make ample money.
Something that may interest you, won't be of much help though. I went to visit my daughter in Florida last year & wanted to do some fishing. When I went to get a nonresident license the clerk wanted my social security number, caught me off guard, I refused, the clerk got huffy & I stormed off to find a manager. The manager said "Yes, it was required info" but didn't know why. I told her that they shouldn't be asking for info verbally, as we are supposed to be protecting this info because there are those among us that are able to do a lot of damage with such info. Bought the license from a different store at a later date by writing the # on paper, still wasn't happy about it. When I got home I wrote a nastygram to Florida fish & game & they told me that the # is required in an effort to track down deadbeats, I think they said it was required by the Feds. California doesn't require it from residents, don't know about nonresidents & I don't know what the difference would be. I'm just concerned about having my # out there cause the darned hackers are becoming more & more sophisticated all the time, don't want anyone stealing my identity.