People prefer zooms.
I can easily understand it. But zooms have also huge disadvantages especially with a x4 range:
The primes are not as complex as a zoom and could really be optimized and for wildlife photography you are anyway at the longer focal length you have at least 95% of the time.
So are primes so bad at all?
Personally I prefer primes, I shot mostly with a 400mm f5.6L until i upgraded to a 500mm f4L.
But walking around with the prime you rapidly become aware that most people shoot with the 100-400mm, (which costs a couple of hundred more than the prime) or with the Sigma 50-500mm or 150-500mm. If people are only going to have one long expensive lens they are going to get the zoom for its versatility.
Long primes are great for nature, but not so good at the zoo or airshows