You think top players are in ECRL on the girls side?? To my surprise, some really good players and teams still left in GA, but the vast majority of the top players and teams are in ECNL on the girls side.
You miss the point. On the boys side MLS is the process of dividing so the top flight are the academy teams that play each other in league. The rest of the MLS Next teams not affiliated with academies are put in separate divisions as they get older. So the truly elite players on the boys side are now playing for the academy side. The rest of the teams play each other and are used as training fodder for the academy teams.
ECNL on the girls side (like MLS Next) is so vast that the truly elite players are intermixed with other top players. They don't really have an elite league to develop the handful of girls which will go on to the USWNT or the pros, unlike the boys. If there were (because there are fewer women's pro opportunities than the men's) it would be much smaller than the boys elite league. But as a result, even just ECNL (never mind GA/DPL/ECRL) is the wild west.