Most of them sound like they might have a large amount of false positives if turned on for an existing code base (a "false positive" in this case would be a case where you would dismiss the warning after investigation). A large amount of warnings that don't point to "actual problems" causes people to ignore or overlook the actually important warnings.

(I'm not saying that these warnings are pointless, but you can have a bug-free code base that triggers a lot of these)