As I have often stated, the reason the regular Next Teams are needed as the fodder. If there were a uniform HS season around the country, you might pursuade the academies, hey for the next 2 months you'll be on your own and continue your national schedule. But 1. MLS Next is not structured for the regular teams....it's their for the academies....that's the deal (otherwise you are welcome to play ECNL)...that's why it exists, 2. the academies (and not just the regular MLS Next teams) are the ones that would scream the loudest at losing said cannon fodder and 3. Even if that weren't the case, there isn't a national schedule for soccer so you'll have some academy teams beholden to 1 and some academy teams beholden to another. The only real days that work nationally for a HS soccer break are September-November, which is why football has them. You could cobble together late April-May but than runs into the invitationals for the European academies so that would never be picked. ECNL on the boys side can manage it because their schedules are regional at least at the beginning.
It seems to me the real issue is that people want to have their cake (playing at the highest levels with the academies) and eat it too (those players should still get to play high school irrespective of the needs of the academy). Unlike the girl's side, it's a choice. Don't like it, that's why ECNL is there. If enough people democratically made that choice, ECNL would expand (it's dominant in some places like the Northwest and has picked up some spots like in Texas) and MLS Next regular would shrivel (Socal and Florida to the contrary). Or if you are good enough take the penalty, hope that you are good enough to be immune from punishment and that someone better doesn't come along.
Soccer can't be organized for everyone. It can build professionals, it can build college players or it can accommodate people who want little league and are looking for the trophies. Because of the freakout surrounding the USMNT, we've chosen building professionals is what trumps everything else. Everyone else (whether the issue is playing high school, the age line, or inclusivity) comes second to that.