Why is "subversion" a good thing?

When it is properly done in an O. Henry-style plot twist, it can be a useful storytelling tool. The trouble is, the writer has to be skilled in its implementation, otherwise it comes off as hackneyed and trite - and most of the writers using it these days don't go for the plot twist. They instead use it to describe their typical bait-and-switch tactics of emasculating the male heroes and self-inserting their Mary-Sue heroines that are better than their predecessor in every possible way. It's massively annoying to fans of the original work, but since the fans have no say in the production they can't really do anything about it until the work is already produced - and even then all they can really do is boycott the film/TV show/book/whatever.

Why is "change" a good thing (especially when it doesn't improve jack shit)?

Some change can be good. A "passing of the torch" from an older property to the new generation can be good if done properly (a la Ghostbusters: Afterlife) but their "change" is usually a strip-mining of an IP for its fan-base and a rewriting of the original work while claiming it is a "subversion" of the fans' expectations. They don't want to make new things. They want to destroy the old thing and replace it with the new thing that's compliant with their groupthink worldview. They want to control the property and its fanbase, or they want to destroy it.