I can think of 2 reasons:
Naturalism is the philosophy most promoted in public schools. With some exceptions, people tend to stick with what they're taught in school. Believing in a supernatural being that loves useus used to be a widely accepted and even promoted way to view the universe, even in schools. That is no longer the case. The new standard is to tell children (and adults) that hydrogen + time = YOU; that they're the result of a cosmic accident and that every thought or feeling they've ever had is a chemical reaction. Surely this can swell meaninglessness in people when they want "meaning" to be more than just chemical reactions.
Nihilism is no longer taboo. There was a time in the West where if you were not a church going christianChurch Going Christian you were an outsider, and people don't want to be outsiders. One can reasonably assume that in that time many people adopted a faith-based philosophy not because they truly believed it but because they wanted to fit into their society. Nihilism could be seen as having a comeback not because more people are believing in it, but because more people are no longer afraid to admit it.