I was one of the more prolific posters on DI (my handle there was Juan Rico), but I tired of the site in 2017 and simply stopped posting. It's funny, I just happened to be looking at DU the other day when I saw the post announcing that Skinner was shutting DI down. I took one last look at it before it disappeared.
As to why he got rid of it I can only speculate, but I'm guessing that it was:
A) An embarrassment to him at this point, being so dominated by those on the Right.
B) Not bringing in any dough.
Oh, well. It was fun for a while. And making Hoyt look foolish (not that it was ever that difficult) was always amusing.