The reason most distance runners don't do speed development is because it isn't part of the tradition of distance running training. Also speed development done wrong both burns you out and dramatically increases the chance of injury. Most coaches don't know how to program it and most athletes hate doing it. You basically have to switch your brain from a "love the grind" distance training perspective to "do the bare minimum" sprint training perspective.
The concepts of speed and speed reserve are well established in sprint training and spriting based sports like football, rugby, etc... For example, 100M sprinters use the concept to win races. If your top speed is Y m/s and you can win your heat with 98% of that speed and your competition needs to run 99% of their top speed, then you have a much higher chance to win the final because you stressed your body less in the heats.
Most distance runners do speed work wrong.
1. Any "sprint" over 60m-80m isn't really a sprint. A 80m sprint at full gas is incredibly taxing and even sprinters are very cautious about long sprints at full gas.
2. The time between reps needs to be long. Like at least 2-3 mins long and most distance runners go crazy waiting that long.
3. You need to start slow and have very little volume. Most distance runners would get crazy sore from just the warm up needed to do a top end speed workout. Most distance runners would get 95% of the benefit just from practicing sprint drills.
4. Start way easier than you think when doing top speed and leave at least three reps in reserve. Do about 60% of what you think is needed in any given session but try to do 2 sessions a week to build up those connective tissues and brain circuity.