Big publishers can muscle their ways around. They've got the money after all. Indie devs don't, so we have to stick by rules.
The main problem for indie games is advertising.
If OP chooses to go NSFW, he can't post his work here. He can't post his work on most of conventional sites. Now, there are communities that focus on NSFW titles but crowds that hang around there only want porn and nothing else.
And audiences on conventional sites don't want porn, so it's better to stick to one side than trying to have both of the world.
Not entirely accurate.
From what I've seen most sites allow a certain degree of NSFW content in the games that are allowed on their sites, but each tends to draw their proverbial "line in the sand" in very different & arbitrary places.
When a site lets you sell games like Duke Nukem Forever, Grand Theft Auto V, & The Witcher 3, from the triple A companies. There really isn't much left beyond actual porn flash games, content wise. & that's not even taking into account mods & patches, often available on those sites like Steam Workshop, that take what was an already MA games well past AO.
Furthermore, most of the people who play hentai/porn games, tend to also play other games as well. It's rather like those who read erotica, tend to be readers in general. So it's honestly not accurate to say those on more conventional sites don't want porn/hentai games, but rather that they aren't looking for them on conventional sites.
Though again that line is getting rather blurry, just have a look at some of the games Steam has released in the last twelve months.
The problem for the OP is the inherently fickle nature of the market, & how arbitrary conventional sites, game reviewers, gaming websites are in discerning what is or isn't an porn/hentai game versus just a game intended for Mature Audiences. The OP could make a game with content of about the level of what you would find in any given season of game of thrones, & they might not run into any problems, or they might have their game declared a porn/hentai game.
It sounds like the important thing to figure out is how to avoid or change this. Any ideas?
I honestly don't believe it can be changed, because it is a characteristic inherent to the market.
Gaming publication sites like Kotaku, prominent game reviewers on youtube like Total Biscuit, & game vending sites like Steam will always have a greater voice than some random indie dev just starting out. The number of people who are going to see your facebook page, or ******* page, or youtube demo; are dwarfed by those who will see the opinions from those other sources by rather impressive amounts. Unless you happen to be some kind of E-Celeb prior to making your game.
Additionally game vendors are always going to have arbitrarily different standards both between each other, & even the same vendor in different locations. For example just look how many Hitler mods you can find in Steam Workshops; conquer the world as Hitler in Civilization, kill people as Hitler in Hatred, etcetera, etcetera. Perfectly legal in some countries, not so much in others.
& it's not as though the situation is entirely due to malice or bad faith actions on the part of these actors. There are many any indie game dev, that use the indie route due to how it bypasses annoyances like the ESRB; & by extension blur the lines between porn/hentai games, & adult audience intended games. Because they make games whose sexual elements are as pronounced, as violence & gore is in a game like Mortal Kombat; but they are still actual games, rather than just an interactive skin flick.
It's rather like how television programs like Game of Thrones & Spartacus blurred that line in television, with graphic depictions of sex & violence not usually attempted by even rated R films, yet still having actual plots & well acted scenes. The OP can chose to contribute to that blurring in gaming by making the game they described, but there really is no guarantee anyone here can give them about potential consequences, or that they will get a fair assessment.