it just happens that these two holds too many peoples, thus having major power in politics.
It doesn't just happen, though. It happens because elections aren't representative. In a first-past-the-post system, voters for smaller parties will never get representation. Which means that sometimes they vote tactically for the 'least bad' major party.
Red 50%
Yellow 40%
Green 10%
In FPTP, the outcome would be something like: Red gets 70% of seats, Yellow gets 30%, Green gets nothing.
In PR, the outcome would be: Red gets 50% of seats, Yellow 40%, Green 10%.
But also, under FPTP there are people who want to vote Green, but vote Yellow instead because Green will never win and Yellow are 'less bad' than Red... if we switch to PR, the votes may be more like:
Red 50%
Yellow 35%
Green 15%
... so moving from FPTP to PR not only makes representation more democratic, it also empowers individual voters to vote for their preferred party rather than for a tactical 'least bad' compromise.