The spectacular record-setting performances (and really amazing depth, too) are the result of a confluence of factors. Beyond general progression of the sport and athletes, there are a couple of unique factors that have been present and building for several years, and are the types of things that take a few years to reveal the full benefits.
1. End of Covid lockdowns and alterations - kids had a lot of life and athletic experiences taken away during the pandemic. As a result, as things returned to normal, a lot of kids really appreciated the opportunity to be a part of a group pursuing excellence, and went all-in on the sport. The real payoff occurs after a few years of getting after it with that level of commitment.
2. The Super Spikes (and Super Shoes) - yeah, they've been out for a few years now, and they had an immediate and direct impact on performances. But they also, as has been mentioned by others, altered training. Athletes can do longer sessions because their legs get beat up less within a session. They can probably run more the day or two after because their legs are less beat up, and their trainers are bouncier, too. They are ready for their next big session sooner. All of this had an immediate impact, but it also kept piling up over a few years, and now we are really seeing athletes reap even more benefits.
3. Training - Good coaches at all levels take at least some cues from the best, and a lot of the best groups of the last 5 years, both domestically (Burrito TC, NAU, etc) and internationally (Norwegian method, Cheptegei's group in Uganda, etc) have not shied away from high volume workouts (and high volume overall). Coincidentally, the improved shoe technology has helped tear down some of the fear many HS level coaches might have had regarding the high-volume approach because coaches know/believe the shoes will help their athletes handle it. Again, it had an impact right away, but let it build for a few years as athletes put in more work day after day, week after week...