Why fix something like that, or fix the matte lines and such around the old effects when you can add in "Nooos!" and make doors bigger?
Good question.

The one effect that always bothered me, and I'm not sure why, was during the hanger scene in Jedi when Han and Lando are talking in front of the Falcon and it is clearly a matte painting. I guess it bothers me because in every other Falcon scene up to that point it was always a real prop. I read here long ago that the real prop was damaged and couldn't be used, so why not use CGI to make that backdrop look more realistic?