Coaching distance is a lot more in depth than sprint/throws coaches realize. Sure, some coaches copy the training plans exactly as Magness or Daniels writes them, but there are crappy sprint/throws coaches as well. Anyone that goes through USATF or USTFCCCA education programs knows that all sprint/jump/throws training programs look almost exactly the same, and are essentially copied and pasted one year to the next, regardless of what athletes are being worked with.
For one thing, there is a lot to balance when it comes to training plans. Peaking 3 times a year, for example, requires a ton of careful planning. Also, there is a massive difference between coaching 800 and 10,000 and even steeple, that's a lot more variety than in sprints/jumps/throws. Most distance programs have at least 20 men and 20 women. As rojo mentioned, it's best to have a few different practice times to separate out mid distance from distance, the younger vs. the older runners. etc. Recruiting is competitive and the volume is intense. In season all year, Sunday long runs, meets just about every Satuday.
It's a fallacy that coaching technical events is more challenging...coaches basically just watch a jump/throw and say "next time do this" then send them into the weight room. Everyone responds to sprint/throw training the same way, whereas some distance runners respond better to high mileage, others to low mileage, some respond well to tempo runs, others to hard intervals. There is a hell of a lot more nuance to distance training.