For instance, 10 years ago when the court determined support, it only looked at what the Father's income was. In some state's, it's a percentage of up to 40% of your income if you got a judge that didn't like you. This means if you're 22 and working at Pizza Hut making $8/hour and the judge says for child support you have to have 40% of your wages garnished to pay support would put you well under the poverty line. This is regardless of whether your girlfriend had a cushy corporate gig making $60K a year with full benefits.
Nowadays, there's been a big push for father's rights and father's rights attorneys are becoming a lot more common. The courts are starting to change course on a lot of previous frameworks. For instance, just on the income issue alone, most courts now look at both parents income when deciding child support. What if your girlfriend isn't working? Too bad, the court now takes into account if you have a college degree and basically assigns you a "potential income" based on previous work history and educational background to come to an estimated income.
It's a lot fairer, but there were some really long, painful years being an unwed father and having to pay support.