Styer has demonstrated ability to hold his own in the Mosconi Cup. There aren't many great options past him so hopefully this is just a one-off year where everything went wrong.
Thorpe has shown recent flashes of potential to compete at this level (5th Peri Open, 3rd US Open 10 Ball) but most of his money and top finishes in the past few years have come from bank pool and one pocket events and regional tournaments. He should be showing substantial improvement in major Matchroom and world tournaments to get another chance.
The US team has a clear core of SVB, Gorst, and Woodward for next year. Styer is pretty much a lock if he keeps showing up to Matchroom events and cashing. So that leaves one additional spot.