Presumably, because the people who want to change things do have in-system ways to do so: joining into a new Party, preaching their views, getting elected, growing, until they convince enough people to give them the power they need to change things.

In practice there may be many roadblocks in that, so this isn't absolute. But if that's the case, it's still on the people who notice the roadblocks to convince most everyone these are real. Without that any protest will lack widespread support and be suppressed regardless.