English is the world language, so in theory they should have a bigger market for voice actresses. So their should be no issue. It all comes down to money. Like pretty much everything else in this world.
It's not only money in this case. In Japan it's still relatively normal and to a degree socially accepted to work in these areas. In the west that's not really the case and comparetively few artists are indeed willing to work in the field because they fear it'll influence their future career negatively. It's the same with 2D artists, where many rather prefer non NSFW work, because they don't dare to add NSFW works to their portfolio in fear companies etc. won't hire them afterwards.
So the pool of people is indeed not as big as one may think. At least not as long as we are talking about professionals and not some girls who want to make a quick buck with some semi professional porn.
Edit: What I mean by that is, that in Japan there are literally A list VA who voiced porn but then managed to get important characters in popular (kids) shows like Naruto, Detective Conan, etc. That would never happen in the US.