You sound like someone who doesn't like or understand learning new things. There are objectively better ways of doing things now than there were 10 years ago, and to suggest that we should stick with something just because a lot of man hours have been put into it is idiotic. Just like why houses aren't built out of brick and mortar any more, there are cheaper, more efficient ways of doing things now.
There are also plenty of reasons to not want to run Flash...
Lack of Flash Gives MacBook Air Two Extra Hours of Battery Life
Flash Player : Security Vulnerabilities
If we built buildings the same way we build software the first woodpecker to come along would destroy civilization.
-- Gerald Weinberg
This is also ridiculous. We have woodpeckers and worse in the software world. We have people actively trying to compromise systems and while it causes problems for some, it's hardly catastrophic to the industry as a whole.