So three answers there -
First, most tech companies provide -paid- paternity leave. Which was my point. The burden on most companies isn't the pay for that period of time, it's the loss of capacity.
Second, the companies that object to that loss of capacity often either misunderstand the nature of the work, or have built their teams without any slack and so have set themselves up for failure. In the former, the teams are fine with the person going out even though management doesn't like it; in the latter they aren't, which is why legally mandated parental leave is so important, since otherwise, as we've seen, a badly run company will make it so you can't take time off.
Third, parental leave tends not to affect multiple members of a team at once. PTO and UTO can. Having too open a policy can lead to half a team being gone for a month, in such a way context doesn't transfer well and actually costs the team a whole month, which will have a lot more effect on productivity than one person being gone for a a couple of months. Obviously you can still have a policy that allows people to do it, but it requires thoughtfulness on the part of someone to ensure it still works out. Again, pulling from example, the big pushback I had to having a person formally reduce their hours by 20% is "what happens if multiple people on the team ask for that?" and that's also why it's easier and less risky to the business to have the person take a day off every week, paid. It means that it can be more easily managed if others taking simultaneous time off is a problem, since pay isn't involved (i.e., you can ask the individual to return to 100% hours until everyone else is done with their vacation, say, and then return to 80%, without having their pay also having to seesaw, which is a *process*)