And yet terrorists and other bad actors have still been able to build bombs despite the regulations.

Explosives have to be manufactured, and most require precursors that are hard to come by. More broadly, perhaps the historic argument that we should care about, eg Somalia, because failed states can enable chaos that crosses borders becomes more true???

(*edit - I mean by hosting factories for illicit materials!)

you can cause damage to an electrical grid without any explosions. you can disrupt a highway by dropping spikes. etc