Yeah, NYC/DC would involve either really complicated/expensive on-land right-of-way acquisitions, or development of new underwater tunneling technology to put the tunnels off shore. Plus it's a corridor that's already served by lots of other existing transportation modes: extensive road network, rail, three airports on each end with direct flights from any one on either end to any one on the other, etc. I'm not surprised that there are other options with a higher value proposition.

"infrastructure, technology, regulatory environment and transportation concerns"

I assume the BosWash Acela corridor isn't on there because any potential route would require digging through numerous suburban neighborhoods, each of which has individual property owners that need to be eminent-domained and compensated.