Weird... I have a level 40 character and I'm never attacked by more than 1 or 2 'racers. Never in ten years of playing have I seen that many cliff racers. Are people using a mod that increases the number of spawns or something?
It seems to happen, at least for me, when I'm traveling through the Ashlands or Molag Amor regions under two circumstances - one, I get stuck in a fight that takes a bit longer that I expected and others join in, and, two, when I deliberately bait them by ignoring them for awhile while walking or flying in order to let a group of them follow me. Afterwards, the bodies are spread out in a circle around me, which in a perverse sort of way is rather aesthetically pleasing
I could just as easily be ambushed by a shalk or a kagouti or a rat on any trip somewhere. Sometimes if it's a kwama attacking me, it's so small it takes a bit to look around and find out what's hitting me.
I have the same problem with rats, bats and bees (one mod I use adds them to the game) because they blend in very well with the background and are so small for me to actually see