The problem lies in the fact that Politicians can see no votes for them in fostering Aviation and a lot of negatives for them when an aircraft crashes.
CASA is a creation that absolves politicians from all blame if a large smoking hole appears somewhere. CASA thus sells itself to the politicians as a provider of political insurance.
Anytime a politician queries CASAs seeming inefficiency and incompetence, they are told that if they meddle with anything to do with aviation, then the blame will fall on them when an accident occurs.
Wisely, politicians decide to leave CASA alone.
To put that another way, in America there is an animal called a Skunk. The Skunks natural defence is its ability to exude an absolutely horrible smell when threatened. Wisely, all other animals leave Skunks alone.