Intentionally cause it was crashing the server. "Updated AI jets to not be able to drop bombs to fix crashing issues." this is from 1.5.4.0. changelog.
In regard to topic, bot difficulty is not an issue, it's theirs' spawning patterns. Maps like Grozny STD for example became barely enjoyable when we meet up to 80 bots before capping last capable flag. In contrast, it took us 20 minutes alone to capture the very first flag on Pavlosk Bay STD few days ago, only because entire bot team was like never spawning there. Afterwards, we finished rest of the map in barely over another 20 minutes, since bots were no longer spawning on frontline flags.
Increasing bot difficulty will not solve the problem, it will mask it. And at the same time, just as ZZANG and Keed mentioned, it will more likely just cause new problems. Having Bots with faster reflexes on city or desert maps is one thing. On jungle, forest maps it will be more of annoyance than an actual challenge when bot will shoot you down instantly from several hundred meters distance, behind trees and bushes, after you left cover 1-2 seconds earlier. Increase the difficulty and within days, weeks there will be complaints that it is simply no fun to be gun down by something from another side of the forest.