Why do you think the 1500 was invented?
The first metric tracks were 500 meters, so they chose an obscure new distance that nobody ran, on the good grounds that it was exactly 3 laps. The olympics ended up using the new distance.
But when tracks were switched to 400 meters, the olympics refused for whatever reason to adapt the race to the 400 meter standard, forever condemning the world to run 3 3/4 laps, and making 300 meter repeats easier to do.
High schools don't have modern pentathlon, equestrian dressage, synchronized swimming or rhythmic gymnastics, why should they copy the 1500 either?