The biggest issue is really that the USHL is such a midwestern League that east coast kids are somewhat hesitant to leave too far away from home when the prep schools have historically been a strong route to college hockey. They're also in the QMJHL region, most do not going to go that route and have to play in a place where english is not the native language.
Let's go through MA-born NHL players:
Jack Eichel - USNDTP
Matt Boldy - USNDTP
Matty Beniers - USNDTP
Chris Kreider - Prep School (3 years NCAA)
Kevin Hayes - Prep School (4 years NCAA)
Conor Garland - QMJHL
Charlie Coyle - Prep school then East Coast Junior Hockey (essentially Tier II USA), then 1.5 year of NCAA then bolted mid-season for QMJHL
Frank Vatrano - USNDTP
Noah Hanifin - USNDTP
Conor Sheary - Prep School (4 years NCAA)
John Carlson (although he grew up in New Jersey) - USHL then OHL (after being drafted, was OHL eligible because he moved to Indianapolis prior)
Ryan Donato - Prep School (3 years NCAA)
Matt Grzelcyk - USNDTP
Jimmy Vesey - Prep school then East Coast Junior Hockey (see Coyle) (4 years NCAA)
John Marino - USPHL (I think breakway Tier II, but east-coast based) then USHL (after getting drafted) (3 years NCAA)
Jordan Harris - Prep School (4 years NCAA)
Colin White - USNDTP
Colin Blackwell - Prep School (4 years NCAA)
Part of the issue is the USNDTP is just so all-encompassing of an engulfer of top American talent from all over the country. USA Hockey is essentially getting to hand-select the best 25 players in the country and remove them from the rest of the ecosystem. A lot of the best kids heading into their Age 16 year old season remain the best kids and they get all the USA Hockey resources flushed upon them, so a bunch of them go on to the NHL of course.
For the later bloomers, it's tough. This is a bigger issue as the share of American drafted players has been increasing, there was a time when not being a Top 25 player by that age probably meant you were a longshot, but that's more and more no longer the case. But since you weren't a Top 25 player, you may not be thinking as seriously about the best possible path to making the NHL and your focus is more directed towards college, where the prep schools combo of hockey and academics can put you in a good position to succeed. But this means you're gonna be a bit behind the eight-ball for the ones that do continue to get better and can seriously work towards the NHL, which is why you see the ones that did make it turn out to be much longer term projects.
If there simply was no USNDTP, I think Junior Hockey in the USA could seriously be overhauled in a positive way for the longterm future of a broader base of players than simply the 25 special darlings that earn the USNDTP golden ticket. I imagine the USHL would be more like an overall umbrella organization and there would be multiple functioning leagues representing the Western States, the Midwest and the East Coast. Essentially what you see in Canada with the QMJHL, OHL and WHL. Just expanding the existing USHL probably doesn't work, country is way too spread out to support that kind of travel for junior hockey. The best talent wouldn't get plucked off to USNDTP and would all be going to head to head with each other in a diffused system that gives the "non-Top 25" kids time to catch up prior to the NHL Draft.
In many ways, I think the USA has outgrown the need for a USNDTP, and I think that they can care to sacrifice some U18 tournament success to create a system that is more favorable to a much broader base of players. I know that's never going to happen though, and it'll continue to focus on the exceptional kids and swallowing up many of USA Hockey's resources in the way it does now.