They honestly, should just get in the habit of releasing on Steam period. Censor and chop it up however you have to. Than offer the patch on their website.
Win-Win... right?
That is generally seems the strategy for most localizers.
It's just that games are not guaranteed to get accepted even when censored, so localizes frequently have to pick and choose where to put their resources. You also have to remember the developers themselves might not be open to having their games censored. That is for example the case with
Innocent Grey.
Looking at MangaGamer over the last year or so, things not on Steam include high-school romances (obviously risky), Rance (they probably gave up after the 4D/5 got rejected), and an eroge from Clockup which has a lot of questionable content. Everything else is on Steam.
JAST explicitly has the strategy of using Steam for all ages releases of games where that makes sense, while keeping everything too lewd on their own store. That has worked pretty well for them until now, considering the games they've gotten approved (like ES GOLD), though Muramasa did run into trouble.
Sekai Project/Denpasoft seem to throw everything on Steam, going as far as rewriting story content in nukige to produce something coherent after all the cuts ('Childhood Friends With Benefits' turning into 'Childhood Friends' on Steam). But it doesn't always work out and Kimagure Temptation and Re;Lord 2 were apparently somewhat of an ordeal to get approved. And even then, KT ended up as an AO release despite the cuts.