Your licensing only matters if you are willing to enforce it. That costs lawyer money and a will to spend your time.

This won’t be solved by individuals withholding their content. Everything you have already contributed to (including GitHub, StackOverflow, etc) has already been trained.

The most powerful thing we can do is band together, lobby Congress, and get intellectual property laws changes to support Americans. There’s no way courts have the bandwidth to react to this reactively.