Back then we had, what, Leisure Suit Larry? The only moderately successful pre-mainstream-internet game I can think of is the Lula franchise unless you count soft porn FMV CD games.
The first "porn" game ever was "Softporn adventure", a Western creation from 1981, that sold more or less a copy for every four Apple II sold, which is way more than successful for this time. The early 80's also seen many Western companies dedicated to the creation of "porn" games, like
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, who's the most remembered because their games were really bad. Then when the 90's came, and with them CD-ROM, it's the western porn industry that invaded video games, quickly releasing thousands of titles every years. It was so successful than most of the porn magazines included a "software" section in their publications, when not directly creating a magazine dedicated to them.
The main difference between the Western and Japanese scene don't come from the number of time they exist, nor from the number of titles they released, but from the point of view they had, and still have, on the matter.
For the Japanese scene, it was a market like any others, and most of the now top Japanese companies had "porn" games in their catalogue in their early age, like
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among others. This while for the Western scene, it was niche games and they never really invested in their development. One of the companies at this time, don't remember its name, even solely sold their games to adults places, for them to be played on arcades-like devices.
This said, in the 90's, when the porn industry take its share of the market, the quality was here, but they never really understood what those games should be. And while the Japanese scenes had games like
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, to take only one, the Western scenes mostly had games full of porn clips and were more on the side of "sex simulator" or "make your own porn movie", than on the side of games.
Thinking that the Western scene effectively started in the 00's with flash games, and had nothing more than Leisure Suit Larry at this time is underrating it. The 00's is the time where the scene started to effectively reach the general public, and those flash games how they did it, but it was just a continuity of the scene. In a way it's also the proof that Western companies weren't totally wrong by seeing this as a niche market, at least in the 80's and 90's ; the public already had, since a decade, all it needed to know about those games, and just didn't tried to find them.
Globally speaking, the West isn't less perverted, just less ready to admit it. Which explain why platforms like Patreon marked the effective start of a more professional (relatively speaking) approach of those games. Simply because with them you can find your dope anonymously, in the middle of the night, from the secrecy of your home, while everybody else is sleeping. This while Japaneses see less problem in the fact to enter a shop, and buy porn material in it.