Frankly, I think we should be impressed. It's a borderline miracle that it's survived as well as it has.
Actually they did. The Federalist papers contained some strong warnings that we must strive to prevent factions / parties from taking over. They were painfully aware it was a potential failure mode in the system they were designing.
It also robs the US of a signalling mechanism: there's no way for the Republicans or Democrats to see that they didn't get primary vote share and only recovered it after specific-issue or more focused parties dropped out.
The US desperately needs preferential voting and mandatory voting. The default supposition of the US has to be that there must be exceptional circumstances as to why any individual did not vote.
It's still a two-party system, but then there are also single-issue or hardline minor parties who often have the ability to hold the government hostage on their demands.
I shudder to think what we'd look like if disenfranchising voters were a more viable strategy.
The problem is not that people don't want to vote, it is that people can't vote: voter suppression (e.g. voter roll manipulation, ID requirements abused to specifically target PoC) or people working two/more jobs combined with the fact the US unlike almost all other countries do not vote on a Sunday or have it a national holiday are quite powerful.
To add to that mix, mail-in voting is not accessible by default for everyone, and extreme gerrymandering (local/state elections) and the "electoral college" system (presidential elections) make it effectively moot to vote in states that are either hard blue or hard red.
As you say, the US constitution was one of the first attempts at a constitution in the modern period. The people who wrote it were not experts on writing constitutions, and could not benefit from the experience of previous constitutions. It should not be at all surprising that it isn't very good.