Dunno if anything has changed in the last few years, but there was a tendency for Japanese courts to sporadically and randomly "make examples" out of individuals by slapping them with absurd fines and threatening prison time. Last time I heard about it some hentai artist was fined somewhere in the range of 10,000$ even though their work was censored, because the judge didn't think it was censored "enough". And even providing evidence of far less censored stuff being available from the same publisher and in the same stores as their work didn't matter. I think neither the store nor the publishing company got fined, just specifically the artist.I'm not sure JP dev can't put their work on their own on Steam.
The problem is that it need lot of work to get teh game aprroved by Steam, so since they can sell it localy through other platform quite easily (Dlsite, FANZA, Getchu....) - why bother ?
3rd party do both the translation and the Steam approval work.
As for the censorship, it's a legal obligation in Japan.
Dunno what the law exactly say, but I think that IF the dev sell the work through Steam, even if it's only outside of Japan, it need censor. If it's a 3rd party based outside of Japan that sell the game only outside of Japan, the censorship is not mandatory anymore (don't mean all dev will rework the original CG to decensor them).
So there's always an air of fear in regards to who is going to be targeted next.
There was also the "
You must be registered to see the links
" incident, which sounds absurd beginning to end.