The 11th man on an NBA roster would be the premier athlete on the majority of teams back in the 80s or 90s. Guys that don't even get in games are boasting 40 inch verts and insane shuttle times all while maintaining ridiculous frames. Why? Because guys have access to what would've been extremely privileged training, supplements, and workout regiments that either didn't exist a few years back or wasn't available behind your favorite gym. All that is awesome - but the conditioning necessary to maintain all that is at a premium. You've got blue chip guys in high school that can squat 480 and bang off vert that have never heard of hip flexor.
Guys are doing everything they can to be fastest, strongest, most explosive - but have zero education, training, or most importantly oversight/support when it comes to maintaining that or preventing injuries while performing at that hyper elite level.
I'm speaking from first hand experience as well. Back in high school, I had the same basketball coach as David Noel and access to a ton of shyt nutrition-wise that I'd probably never be able to see had my dad not been cool with David West and Rodney Rogers. And entirely because of that of that exposure I was the fastest person I knew until I got to college by a long shot. I could beat people up on the court because I was just flatout stronger and quicker, skill be damned. Shredded my knees for life because the entire purpose of high school development and training is to simply get to the next level. In college, depending on where you go, there's almost no oversight or conditioning beyond staying in 'basketball shape' to survive the season. Long term conditioning, stability, muscular endurance... those things don't simply exist without someone going out of their way to make sure you're taken care of (and that they're taken care of by extension).
Long story short... in high school and college, you train simply to get to the next level. Long term conditioning for today's generation of athletes should begin long before the pros (shout out to futbol)