Did anything prevent them from transitioning undefined behavior towards defined behavior over time?
> It's that there was live C code in the world that did this stuff, for real and valid reasons.
If you allow undefined behavior, then you can move towards a more strictly defined behavior without any forward compatibility risk without breaking all live C code. For instance in the `EraseAll` example you can define the behavior in a more useful way rather than saying 'anything at all is allowed'.
No, and that has been happening over time. C++26 for example looked at uninitialized variables and defined them. The default is intentionally unreasonable for all cases where this would happen just forcing everyone to initialize (and also because the value is unreasonable makes it easy for runtime tools to detect the issue when the compiler cannot)
> It's that there was live C code in the world that did this stuff, for real and valid reasons.
If you allow undefined behavior, then you can move towards a more strictly defined behavior without any forward compatibility risk without breaking all live C code. For instance in the `EraseAll` example you can define the behavior in a more useful way rather than saying 'anything at all is allowed'.