All due to Ordinal voting. First Past the Post is the simplest Ordinal system, and completely broken if you have more than two candidates.
The only solution is a Cardinal voting system. Cardinal systems can handle two or twenty candidates without issues. Approval or STAR are the best options.
The sad part is, in 1780, First Past the Post was the only system available. It had to be adopted before mathematicians could look at it and say, hey shits broken.
The first was Condorcet. A French Mathematician who noticed the first problem with Plurality in the 1780s. But if you know your history, you'll know that being a French Nobleman in the 1780s was not the healthiest thing to be, regardless of how fucking based you were.
As an aside here, Condorcet was fucking based. He was antislavery, and argued for full suffrage for both women and the slaves that he wanted to free. He argued for universal education for all, and thought it would solve so many problems.
Anyway the next guy who saw the problem with Plurality was another French Mathematician and political scientist named Durverger. He proved that First Past the Post voting will always result in two party dominance. And he proved this in the 1950s. So not much to be done about it.
The next guy to put his name to voting science was Kenneth Arrow, an American who in the 1970s, showed that all Ordinal voting systems were flawed.
But again, the data came in far too late to easily fix things.
So here we are. The saying goes, the best time to plant a tree was 20 year ago, the next best time is now. So call your local representative and ask them to sponsor a switch of voting system to Approval or STAR.