User blog comment:Lykrast/A suggestion about Flash/@comment-2112140-20130710170415/@comment-8506165-20130712155422

"making spells directly counter other spells (Target cannot use Flash while Exhausted) would be imbalanced cause it would punish the player for picking a spell."

You're already punished for not picking Flash because the only way to counter Flash is Flash. If you're a jungler and Smite is a must-have or if you're a support and you need Exhaust (for instance) or if there are just other spells that are too good to pass up on your champion in particular, you're left with a dilemma - take Flash and have no choice whatsoever in summoner spells, or not take Flash and have to deal with the fact that everyone else has it.