Also motivation and incentives. The reason we haven't seen many drone attacks on civilians is that it is far more lucrative to get civilians to buy your product than to kill them, and the companies that actually have the resources to mount a credible drone attack are making a lot more money doing the former.
Terrorism in general has always been far more overhyped than actually a problem - the median number of terrorist deaths per year in the U.S. from 1970-2020 is 4, making your odds of being killed in a terrorist attack significantly lower than being struck by lightning. And the reason is simply that it's deeply irrational. What do you have to gain from killing a random stranger?