It's an inevitable conclusion of our winner take all voting system. "The man with the most votes wins." If 4 candidates run, and they get 22% 22% 16% and 40% of the vote, the man with 40% of the vote wins the race, and 60% of the population didn't get the candidate they voted for.

Now imagine you've got a red, orange, green and blue party. Orange voters get together and decide "You know, the Red party's platform is pretty similar to ours, what if we didn't run a candidate next time and instead encouraged our voters to vote for the Red candidate instead? The blue candidate won with 40% of the vote, but our two parties put together would have 44%.

In the next election with three candidates, the red candidate wins 44% to 40%, prompting a similar conversation at the Green party headquarters. Soon enough there are two parties.

We're one of if not the oldest representative democracy in the world today; our constitution is 250 years old, there's some old bugs still in the code base.