Simple, as you should know, blizzard ban ppl in waves for botting. there can be many months between the big ban waves. Other cheating like teleportation, speedhack, exploiting, is banned on the spot. Dont you think that it would be stupid to ban bot programs on the spot? would be too easy to see whether your program is detectable or not. Bot bans from player reports, are made on the spot aswell, where software detection is done in waves.
The fact that you choose to make your bot in autoit with its limitations, clearly shows that perhaps it is you who doesnt understand how thigns work...