The party loss after Mulroney was, IMO, primarily due to the during reform party - a division of the conservative party. If you look at voting percentages, the conservatives still claimed 30% of the vote, just divided differently.
The bigger difference I see is that Mulroney had managed to win nonconservative votes, which then left during the 93 election.
That means those liberal voters you claim never bote anything else voted VERY strongly against the liberal party and for the conservatives to give Mulroney his wins.
From my knowledge, the NDP has never been wiped out. They've been reduced down to a few seats, much like any other party, but they're still the NDP. Liberals in Ontario were gutted entirely, not dissimilar to any of your conservative examples above, and lost official party status after nearly 15 years in power. Despite how awful Ford has been, they STILL haven't clawed back to even a shadow of a party. If that isn't an example of them being destroyed in public opinion I don't know what is.