Canada

This makes sense if you relabel the BC Conservatives on that graph as BC Liberals. It’s really just a story about the Liberals.

The BC Liberals were one of the major BC political parties. Despite the name, they had no relationship with the federal Liberal party. The BC party was significantly more to the right compared to the federal party. As a result, they captured a ton of centre and almost all of the right-leaning votes. This went on for decades.

Once the BC Liberals got defeated by the NDP, some weird stuff started happening. First they renamed their party from the BC Liberal Party to the BC United Party. This is almost certainly only because Justin Trudeau’s approval rating started sliding, and the BC party wanted to avoid getting a bad rep by name association.

Then they discovered that their existing leadership was actually super unlikable, and MLAs started declaring they would run as independents. Some outright declared for the BC Conservatives (who were, up until this point, a fringe party that didn’t win seats). That created some momentum and more MLAs started jumping ship.

BC United finally collapsed a couple of weeks ago. The party is effectively dead and I don’t think they’re even trying to win any seats next time around.

The situation is analogous to a local burger shop getting bought out and replaced by a Wendy’s. You could ask why Wendy’s is all of a sudden so popular, but the answer has less to do with Wendy’s being popular and more to do with them serving similar food as a previous burger joint, and since they’re in the same location, the same customers keep coming in.