Tuition fees have been capped, not tuition costs. Tuition costs go up when universities build more buildings, hire more staff, pay for more electricity and heating. If they’re doing all that stuff to cater to extremely lucrative international students who then get cut off, the school ends up with budget shortfalls.
This is all excess capacity (and luxury) that domestic students don’t need and didn’t ask for. It’s all designed to compete for international students on the global market.