Because that is an escalation that nobody wants, for now. Even piracy was tolerated for a while until it became economically too disturbing. I don't think it all disappeared but it is not that bothersome.

If anybody started threatening commercial civilian flight, countries would fall on them like bricks. Quarantine for a few months was devastating on many fronts. Now, think if all flights were grounded for months...

The only thing I can think of is that the places where it's relatively easier to get explosives (war zones like Iraq, Afganistan, or Syria) doesn't overlap much with places where it's easy to get powerful drones (developed countries).