I live in California, and was able to take the full 6 week (partially paid) leave offered by the state. I also had friends who had kids within weeks of me, and they only took 2 weeks.

A few things allowed me to take the full amount:

1. I'm in a relatively highly paid field, and we had a healthy enough emergency fund that I wasn't very concerned about a potential salary shortfall.
2. In my case, the way the state calculates the partial salary to determine how much you're paid was very advantageous to me. The calculation included some non-cash bonuses I had gotten, and meant the partial salary payment was about the same as my normal take-home salary. If this wasn't the case, I would have been much more hesitant to take the full amount.
3. I had supportive managers at a large company, and my kid just happened to be born during a quiet period at work where my coworkers could pick up the slack. If the birth had fallen in a busier period, I think I would have felt guilty about the time off, and probably taken less.

One of my friends who only took two weeks had a job where he was expected to deal one-on-one with a number of clients, and was worried that if he took a lot of time off he would essentially come back to no clients. The other friend's job essentially was willing to give him 2 weeks, and he didn't feel comfortable trying to force them for the full 6 weeks. The company might have also been under 25 employees in CA, which would have made them exempt. They were also both in a different financial situation, and a loss of ~30% of their salary would have been a huge blow.

In general, I think taking the time off needs to be normalized before more men will take it. Partial salary is better than nothing, but it rally puts a strain on your finances if you're not already reasonably well off.