For that matter, the drones don't solve any problem real-world terrorists really have. They are usually discovered while planning attacks or acquiring weapons and explosives. Putting a bomb near a lot of people is comparatively easy.
Maybe ANFO bombs aren't that powerful, but those can't be the only easy options for DIY bombs.
I don't really see how it's a useful priority to try to physically stop terrorist attacks. There obviously aren't that many people who successfully commit them (because the number of related deaths is tiny) and the talk of "well we're stopping a load of them you just don't know because it's classified", yeah... they say that, but why should I believe unqualified statements about other people's secrets?
Why not focus on the factors that make people radicalize, and work on reducing those?
I guess it makes shitty headlines compared to "Kevlar-coated military drone hunting eagles kick evil khaki-person ass".
Also buying the large quantities of DIY explosive components needed to build large bombs will raise red flags.