Also, a majority of the tools available for developers to license would turn off potential players, and not for the "I want to bot/hack/whatever" reasons.
Lets use
nProtect GameGuard as an example. Right after I purchased Aion (yes, yes, most wasted 40$ in my life, I agree) I got banned. It took nearly two weeks to get NCSoft to unban me. What got me banned? The fact that I have a free web server software package called XAMPP running on my PC most of the time. The software saw Apache and mySQL as hacking software. Shaiya also banned me - but it saw my
antivirus as the issue (and they never did unban me). If I see that a game is using GameGuard, I personally will not touch it, no matter how interesting or intriguing the game appears.
Added to that, the majority of these bot prevention systems act like a rootkit and they
violate a users privacy. That turns off many, many people. And, in most cases, they are easy to bypass. Blizzards Warden? Cracked and bypassed a day after launch. I can think of two pieces of software currently used to cheat and bot in World of Warcraft right off the top of my head, that bypass the games protection.