Welcome to the parliamentary party system. There are some votes you can avoid the party line with, but if the whip declares it a party vote, it's a party vote and you won't get your party endorsement for the next election if you step out of line.

Once FPTP voting is done and there's a majority, it's pretty much a party dictatorship after that. Caucus decides what legislation will be enacted, and the caucus/cabinet is chosen by the leader. Any debate in the legislature is purely for show, and sometimes they'll take suggestions/amendments from the floor, but usually not.

It's another stupid system that barely beats a monarchy.