US distance running was atrocious in the 90's/early 2000's. For some reason, we became obsessed with running less mileage and doing more speedwork and the results were terrible. If im not mistaken, there was a year in the '90s where not a single HS runner broke 9 in the 2 mile.
Hall/Ritz/Webb + Dyestat and Letsrun led a revolution during the 2000's. In recent years, social media & Youtube have democratized the dissemination of training information for coaches and athletes. Anyone with an internet connection can see what the top guys are doing, and apply it to their own training. My coach in HS didn't even know what a tempo run was, there is absolutely no excuse for that these days with all the information available. And sure, spikes explain some of the impact, but only a small amount.