

It does make sense though. The main motivator for politicians is power. That means, naturally political systems flow towards maximizing power for those in power, that’s just the natural progression.
To change this, major political upheavals are necessary, so basically events where the whole old leadership is tossed out and the new leadership can try to setup something to stop the same thing from happening again.
WW2 was perfect for that. All those countries were in need of a completely new political system and thus they could be built better from the ground up.
The US never had any event like that (apart maybe from the civil war).
To change the system without such an event, two thirds of all relevant politicians would have to vote for changing the system that brought them to power. Not likely to happen.
Fair.