Logistically speaking, the size/weight of improvised explosives that deliver results terrorists are looking for are typically too heavy for small drones. Terror devices also typically employ various amounts of miscellaneous shrapnel, to get the most effect out of limited explosive power, but also significantly increasing payload weight. To make any use out of explosives that weigh enough to let the drone still be pretty fast, you'd have to swarm them. That'd be a pretty effective tactic, but it obviates the benefit of drones over just using any other long range weaponry, precision guidance. If you're just going to spray and pray, do it with something bigger. For super precision individual strikes, a racing drone could maybe take out small targets, 1-3 people, but that's not a terrorists target. And even worse for those cases, they're extremely loud and easy to spot, they wouldn't be too difficult to evade. They're fast and nimble but that's relative, you're looking at 60mph averages, especially with a payload. You can dodge a 60mph car, you can probably dodge a 60mph drone.
They're honestly most effective in Ukraine because Russia is just terribly incompetent. For military use they're effective at rendering stationary equipment inoperable, or taking out a lead truck in a convoy, or blowing up an ammo depot. They're easily deflected with proper equipment since we know what tech they're using (2.4ghz or 900/433mhz control links, 5.8ghz video links), Jamming them is actually easy, just Russia sucks and can't wipe its ass and shit on its elbow at the same time. If they had enough explosive capability to, say, blow up a bridge, you can bet the Kerch Straight bridge would be gone by now.