Not sure if this is still the case, but I remember dynamite on the ground being harder to spot with high trap skill. With 300 traps placing a mine would mean it's impossible to spot them for most players.
It was the case as of pre-wipe 2012 (Voland spawned the frag mines everywhere... including respawn tents...), and players activated them. So yeah, it probably hasn't changed. With 300 traps skill, literally no player would be able to see the mine, not even the person that dropped it from 0 hexes with 10 PE. And it did probably the same range of damage as Dynamite.
So yeah, it would just be overpowered in unguarded towns, and a griefing tool in guarded towns. I think that they were planned to be included in "Domination", but that feature seems worlds away.
I don't agree with getting detonator parts from them either, though. Maybe have the parts be available in BH too, but just having a Traps alt go around and collect the det. parts in random encounters is not what I think of a good feature... I think blueprints are an unexciting, unneeded waste of time too, but that's different issue...