BC tends to be a two party province (as far as I know, Ontario is the only province that maintains three strong provincial parties).  For quite a while, those two parties were Social Credit and NDP. Then van der Zalm managed to destroy Social Credit and the Liberals displaced them. The BC Social Credit party always included both federal Liberals and federal Conservatives, and the BC Liberals have effectively the same coalition. The political opportunists from the center and right tend to coalesce in whichever party can successfully oppose the NDP.

There is still a BC Conservative party; it is very small and is kept limping along by a few ideological purists who do not like the "big tent" of the BC Liberals.