The reason why we still use PWR is because of pilotability. When you're able to modulate the power of a reactor of 40% in 30 minutes without damaging anything or engaging any failsafe, you can reasonably make nuclear reactor follow the consumption.
The reason we mainly use PWR is because the military wanted them for submarines and the government and industry had a massive program them into commercial use. From there we got a large amount of legacy, knowledge and infrastructure around them.
After 3 Mile Island the nuclear regulatory system changed and regulation were made technology specific. So even if you wanted it would be practically impossible to get a license for anything else. Thankfully this has now been realized and they are changing their regulation to make them less technology specific.