I think another problem was advertising,
More than a question of advertising, it's a possibility to advertise. It's games, but it don't just include porn content, it include small porn movies... It's obvious that you'll not be able to advertise for those games as you would for any other video game.
I have the chance to live in a country relatively lax when it come to adult content. One or two months after XXX studios started to make games, we already had one magazine dedicated to them ; then, from memory, two others followed. One was even sold with computer magazines, because only showing censored content. The other(s) was/were sold with magazines like Playboy, so less visible unless you were already searching for lewd content.
We also had a company that specialized in selling games through mail orders, that had a part of its catalog dedicated to those games.
But in countries more strict, I guess that either you spent tons of money to advertise in Playboy (ads surely cost a lot), or you were limited to purely porn magazines and some ads in sex shops.
This being said, they were doing it for a bit more than ten years, so I guess that they still achieved to reach a bug enough part of their public.
Even on the BBS we passed around the basic animated clips or the "favorite topless celeb" disks but didn't know about the others, so advertising and word of mouth failed there.
They were too big for BBS. Movie compression wasn't as efficient that it is now and like those games relied mostly in videos. I haven't really looked, or if I had I forgot, but I guess that most used the 700MB available in a CD. Imagine downloading this from a BBS at a range going from 14,400bps to 56,600bps, depending of your modem.