Probably because many (most?) such people believe that markets are closer to a random walk than not. And beyond that, they probably believe that if you find "alpha", it will always be short-lived because over time the market will price in the effects of your trading decisions. If that's true (and I'm not saying it is) then you're looking at constantly spinning the gerbil cage, to not necessarily make much progress.
I think it's also believed (known?) that to do the real good stuff with HFT and what-not, you need very expensive server co-location and peering connections to minimize latency to the highest possible degree. A lot of people probably aren't interested in doing all that, or can't afford it, or just don't know how to get started in that world.
I think it's also believed (known?) that to do the real good stuff with HFT and what-not, you need very expensive server co-location and peering connections to minimize latency to the highest possible degree. A lot of people probably aren't interested in doing all that, or can't afford it, or just don't know how to get started in that world.