This is deliberate. To my knowledge, absolutely no US airports allow you to transit without going through immigration, and stopovers in the US are very hard to avoid because the FAA imposes a hefty fee to flights over the country unless they stop at a US airport.
So it's very expensive to overfly the US without landing, and once you land you can't avoid immigration even if you are just transiting on your way to another country.
> the FAA imposes a hefty fee to flights over the country
The overland fee is $61.75 per 100 nautical miles (and it's a lower $26.51 per 100 nautical miles)[1]. Is this really that high? Let's say a flight from Canada to Mexico has to cross 1600 nautical miles overland the US. That would cost 16 x 61.75 = $988. Isn't that pretty low? On a flight with 200 passengers, that's an extra $5 per passenger.
They require issuance of paper visas and an in-person interview. It's _easier_ than B1/B2 visas; but in the overall scheme of things not _that_ much easier.
For a person deliberately avoiding the US (whether out of principle or otherwise), I can't imagine a trip through customs for a transfer would be acceptable either.
So it's very expensive to overfly the US without landing, and once you land you can't avoid immigration even if you are just transiting on your way to another country.