It's not like women currently in the profession are going to get paid more in this situation. Increasing the talent pool drives wages down. If you do this via H-1B or attempting to reduce barriers to women, you get the same results.
The OP wanted to know why everybody is making a giant fuss about it. It's not because companies suddenly developed a moral compass, but rather they figured out how to dovetail a "win-win" by adopting the cause. They get good PR, diversity increases, talent pool increases... but most importantly: costs go down.
There's no way to fight against this sort of wage suppression other than unionization, so if sexists want to use this as an argument, they'll just look like... sexists?