COCKS OF THE WALK
Well, I live in France where the "two-tribe" (Left and Right) system is also predominant. And whyzzat?
Because before "two-tribe politic" any number more than two required a highly-multiple
majority of parties to pass legislation. That can be tantamount to a "miracle" given the wide differences in political opinion that even "alike" parties (that is, are similar) may come to a bitter stand-off due to some arcane differences of opinion. (A prime example of that is Italy where governments break-apart easily and are very difficult to build amongst Italy's multiple party-political-system.)
The two-party system has its constraints, but they are perhaps less "constraining" than a country run by multiple parties ... especially because of the "Latin-males" (France, Italy, Spain and Portugal). They have a strong tendency to think they are
cocks-of-the-walk ...