The majority scholarly opinion is that women are allowed to go to the mosque while menstruating, the ones who don't say it's because leaking blood is unsanitary, however that is nullified in this day and age.

You're correct women don't need to pray while menstruating. This is because Muslims need to do a ritual purification before prayer. Things that break this purified state include sleeping, farting, and any liquid or solid matter that comes out of the body. Obviously this includes menstruating women.

However the difference is that menstruating women are not missing prayer it is simply not required of them, just how it wouldn't be required for them to fast. They get any reward for prayer despite not having to perform it. I don't see how any muslim women would think this is oppressive.