https://en.wikipedia.org/wiki/Two-party_system
Maybe Americans should question why new parties cannot be formed that actually represent their people instead of looking to replace democracy entirely with...a lottery? I can't comment further because I am not American.
However, NZ has a proportional voting system that leads to coalitions forming governments. This is considered a good thing, but can lead to…interesting outcomes. The current government is very much the dog being wagged by a couple of nasty tails. Current PM is a weak “I've run a company so can run a country” type.
Hopefully a successful company, that is.
His management experience at Air NZ has not correlated with strong leadership. Compare him with the previous PM (Jacinda Ardern) and most Kiwis, even the right, would agree she handled things better. A few lefties like myself think she could have done more (especially wrt to housing policy) with the immense political capital she had just before Covid, but oh well.
You didn't ask for any of that sorry!
Denmark seems to be pretty solidly Venstre vs the Social Democrats since the mid nineties with many other parties.
Israel is genuinely multiparty, with a rule that Benjamin Netanyahu must be returned every few years.
Germany is multiparty on paper like Ireland but is dominated by the Christian Democrats and the SPD at federal level. Every Bundeskanzler of West Germany and post-reunification Germany comes from these two. Ditto every president except Gauck.
In mamy countries, there is a level of nepotism with close relatives of former political figures taking charge. Canada, the USA, India, Greece and Thailand have all had this, with some of the same names repeating over the course of generations.