Actually, you do hear about the Kenyans doing loads of plyos and drills, some after nearly EVERY run.
Plyos are hugely improtant and an excellent derivative of pure speed.
They force use to use exaggerated range of motion and/or overspeed movements to improve specific neuromuscular patterns and biomechanical portions of the running stride.
For instance, high knees, hill bounding, and hill hops are all explosive drills designed to improve the explosive power of the foot strike and knee drive along with improving ankle power and flexibility.
Drills like quick steps or 40-50m downhill sprints at nearly 100% effort in effect teach your body to run faster than it can.
You can go to a 200m downhill grassy surface and run 22 seconds. If your PR on the track is 23.5, you have bgun the process of creating new neuromuscular patterns to improve speed.
Anyway, plyos and drills are very important. Note many interviews with top guys such as Geb praising their use.
Also, hill running is in effect a plyo of its own.