This is the key insight, and I'm left asking why. As someone else said, it's at least as much about being entertaining as about being relatable. So why in running are the influencers SO FAR from being elite athletes?
As a hypothetical, I don't know any "baseball influencers", but what would people want to see? Probably something like "life in the MLB" or at least "my dream to play college baseball and then make the minors". It's unimaginable that people would watch a channel that's just a guy playing in some casual softball league, unless it's somehow a joke.
The same is true of any sport that I can think of. For swimming, it's not the lap swimmer at the rec who gets attention, it's the pro or top college swimmer. For cycling, the same. Even for triathlon, which has a lot in common with road running, many of the big influencers are top pros, and if you're an amateur, you should be at least making Kona or something (call that a 2:30 marathon, adjusted for age).
So what makes running different?