In principle, they are not enabled by default because a C compiler must be able to compile standard C by default. One practical reason I can think of is becaus

In principle, they are not enabled by default because a C compiler must be able to compile standard C by default. One practical reason I can think of is because not everyone compiles their own code. You must most definitely look for and enable such flags as they become available in your own projects. (eg I was rooting for -Wlifetime but it did not land for various reasons) But when you compile other people's code, your breaking your local build doesn't help anyone. Best you can do is to submit a bug report, which may or may not be ignored.