But they are really limited in their ability to respond adaptively to unforeseen circumstances. That's where pilots come in.

To replace pilots, you need

a) A computer which is smart enough (doesn't exist yet)
b) A very expensive hardware system to ensure the computer can execute it's desires reliably, all maintained to nasa standards...$$$$$$$$$$$$$$$$

Predators are cheap, but they don't have a good survival rate. If 737's had the same operational statistics, we would have crashed almost 2000 of them in the last ten years...even the most oblivious John Q Public would have sat up and noticed THAT.