Spyderco's 8Cr13Mov is near the top of the class for 8Cr13Mov but that's not really saying much. The performance of this steel just isn't great relative to better budget steels such as 9Cr18Mov, 14C28N, or D2. People sometimes praise it for being quick or easy to sharpen to a good fine edge. While it can hold on to a ho-hum working edge for a while, it loses that impressive fine edge fairly quickly. I think that's a big part of the hate for this steel.
In the specific case of Spyderco, a big issue is price. You can get lots of knives in 8Cr13Mov for half as much or less. With so many companies offering better budget steels for less, that 8Cr13Mov sticks out like a sore thumb. Compare it to a Civivi or Sencut knife in 9Cr18Mov. It's much better steel with an exceptional heat treatment, in a quality knife with great action, for around $40.