It makes less sense for American's to do the full DL circuit if their contracts and appearance fees they would get elsewhere are a much larger function compared to what they would get in prize money at a DL. I understand, as fans, we want the stars all competing. But athletes will just stay home and train for the championships because their placing, time, at the globals or bonuses if they medal makes the the DL prize money look insigificant. Unless more prize money is offered, DL or not, athletes will peak for the championships and dedicated time trials.
Also, contracts are getting higher, even accounting for inflation, for American athletes at least. There's more opportunities now at each teir of pro running. 20 years ago, there wasn't much ROI on athletes, they didn't promote products the way they do now so your average runner cared nothing about brand. People just got a pair of Asics, New Balance or whatever and ran. Now shoes and even running gear is being promoted significatly more. Nike accelerated this in 2015 when they brought science into running shoes after only being decent at it pertained to the Pegasus. Now companies are bringing science into running gear. People bought in to Nike koolaid, companies had to follow, and now shoe lineups for companies are deeper than ever. People who don't even run are buying running shoes casually at levels I've never seen before.
Part of it is advancements in social media and notice how being marketable is a huge factor in contracts, especially if you aren't top teir coming out of college. Instagram influencers make more money than full time pro's putting in 100+ mpw and brutal workouts. Think about that. Now the NCAA has incorporated NIL. Runners of all levels can be a lot more interactive and relatable to proffesional athletes compared to other sports.
Okay, the athlete-company ROI might be insignificant for a few companies like Nike who are invested in much more popular sports in America, but I wouldn't be surprised if it's true Nike is scaling back on contracts offers, thier relative profitability has probably been the largest over the past 7 years and no company has put out anything better than the Alphafly/Dragonfly still. They are fine for now. For other companies though, the ROI is becoming more noticeable.