Once you hit the 4 hour mark for travel time, ridership craters. That means at around 500-600 miles (just because the top speed is 220mph doesn't mean the train averages that speed), it's infeasible to have service, especially if you don't have the ability to hook multiple cities up on the line. DC to Boston is on the long edge of this line, but the DC-Boston route services every combination of DC, Baltimore, Philly, NYC, Boston at no extra marginal cost, so it's worth it.
You also need to have evidence of strong existing demand between city pairs (this is basically Florida's problem; there's just not enough travel between its major cities), and you also want a decent urban mass transit system (this is where Texas suffers).
Hitting 220mph service needs dedicated track--you can't mix trains of different speed regimes on the same track without very strict schedule reliability, and the US just doesn't have that reliability. 125mph is more doable, if you have ample opportunity to do the passing, although you still need better reliability than the US sees now. The Midwest just doesn't have the demand to justify building dedicated track, so it's not worth 220mph service.
Yes, Acela is not true HSR, and it's a crying shame because the NEC is the best, or very nearly the best, place in the world to put HSR. But outside of the NEC, the US is simply too big, and its major cities simply too far apart from each other, to put HSR in.