I am surprised Poring didn't mention this in in his ending message but yeah, this was 100 percent Steam's fault.
That just isn't true, here's a transcript from pixiv message
"Of course, there are creators with extraordinary perseverance, but I don't think I can afford to spend too much time on the same game.
So I think it's time for Castle to end.
There is the impact of not being able to get it on steam, but I now feel that even if Castle were to be sold on steam, I would probably end up making Castle here in the chapel.
On one hand, I can't stand long term production, on the other hand, I want to try to do other types of games.
Another big problem is that I feel that the content of the game I've made has deviated from what players want.
Looking back at Castle's four stages, I think I did the best job with the Doll House, in terms of content and atmosphere.
As for the Laboratory and the Chapel, I tried to make them more informative at first, but I missed out on what they should have been.
Now that I've gone back and looked at those two stages, it's obvious that they shouldn't have been like that.
But it's impossible for me to redesign them."