The HK legislature and executive aren't democratically elected, but directly or indirectly chosen by Beijing. Moreover, Beijing's control over the legislature was increased when they "reinterpreted" the agreement and removed several pro-democratic legislators a few years ago.
Beijing wants this law passed, Beijing controls the political future of those who with the power to pass the bill. The HK citizenry oppose the bill.
I mean even the protesters are protesting against __their__ legislative council. [0]
[0] "forced the city’s legislature to postpone debate on a widely unpopular bill"