How come blind has such a long cooldown?

While the effects of Blind will interrupt on damage, the ability itself is neither a disease nor can it be dispelled. (Perhaps you're recalling how, at one point in time, Blind was classified as a poison effect?)

Regardless, one of the great strengths of Blind is that it can be used instantly while under pressure. You can use it to neutralize an attacker, to interrupt a healer who would otherwise save your target's life, or to stop an escaping victim in his or her tracks; the list goes on. The three-minute cooldown on Blind helps mitigate its potency and versatility just enough to ensure that the ability isn't spammed or otherwise abused.

Overall, though, between Gouge, Blind, Sap, and other stuns, we feel that rogues currently have very strong CC in both PvE and PvP environments. (But thanks for the feedback!)