Some people think that those in power will put the option to remove their power on a ballot. That's always been confusing, and hilarious to me.

"Never" is a long time. If this were just a game theory world, then yes. If people always did the optimal move, then a multi-party system would eventually become a two-party system, and once it became a two party system, there would be no way to change it because every change is non-optimal.

People sometimes don't behave rationally. In Canada in the 1990s the Progressive Conservative party had a majority government and seemed unstoppable. But, the leader Brian Mulroney became incredibly unpopular. At the end of his time in office, he was so unpopular that everybody knew that his party was going to be destroyed in the next election. But, at that point Canada was effectively a 2-party country, Liberals and Progressive Conservatives. Even though the Liberals were going to take power, it was just a matter of time before it swung back to the Progressive Conservatives. So, the smart move for the PC party would have been to just bide their time.

Instead, the party split in two. Half stayed PC, the other half joined a new party called Reform. But, because of first-past-the-post voting, the conservative votes were split, half went to the Reform party candidate, half went to the PC candidate. As a result, the PC party was destroyed in the election. They went from 169 seats to Liberals' 83 to only having 2 seats. They were the 5th biggest party, after the Bloc Quebecois, Reform, and NDP. They nearly lost official party status.

These days there is no PC party anymore, The split party eventually reformed and dropped the "Progressive", now they're just the Conservative party. And, they're again part of the duopoly. Whenever the Liberals lose, the Conservatives win, and vice versa. But, for a while things changed because humans are not always rational.

It's theoretically possible for humans to be irrational in a good way too. A well meaning and honest party could gain power and then pass legislation that hurt itself and helped democracy, like getting rid of first past the post. But, to do that, they'd need to feel massive pressure from voters. Even if the politicians want to do it, they need to show that the people are forcing their hand.