I'm still only 82 so I haven't really been trapping yet. They could possibly be resisting them, I guess you would have to look at your combat log and see if the mobs are simply resisting the traps or not. That's really the only thing I can think of as to why they wouldn't be going off.
Off Topic:
Browsing MMO-Champ hunter section I was looking at an updated spec/rotation whatever else section.
Am I the only one who thinks this sounds pretty absurd for a BM rotation.
MMO-Champ User wrote:
Basic priority: Hunter’s Mark > Kill Command > Kill Shot > Serpent Sting > Explosive Trap (Trap Launcher) > Arcane Shot (if focus > 75) > Cobra Shot
I can understand using something like trap launcher + trap to force proc LnL but they mentioned nothing of that in their SV section. Also only using Arcane Shot if focus is above 75...Kill Command costs what 40 or 37 if glyphed. That's a lot of waste of focus by having enough for another 2 Arcane's between that 40 and 75 (that's counting regen and talents and what not).
Unless I'm completely missing something I don't see how this is any good.