changed), it could very well simply be the increase in the number of players that are being scouted and evaluated. It's possible that the quality of HS recruits is simply getting better. It's also possible that some players that used to simply get a 2 star thrown on them (or not evaluated at all) are now getting evaluated (due to more camps, etc.) and getting the high 3-star designation.
Frankly, I don't get super caught up in recruiting rankings myself. Yes, the higher the "star"/rating the greater the chance someone could become an impact player. But there are so many things not captured by ratings with regards to system fit, cultural fit, what roles people will play, as well as the "flaws" in ratings systems that rate players based on offers they get, what camps they go to, etc. (which causes some players to fly underneath the radar).