Not to be nitpicky or anything, but how are you imagining lasers? I can't conceive of an implementation having any kind of explosion/K.E. at all. If you're thinking something like what appeared to be a plasma spitting repeater from Terminator (i.e., the future/flashback where a T800 infiltrates a human base, dogs start barking, and it whips out a 2 handed rifle and begins to unload on everything) then maybe I can see where you get the explosion part, but that would more fall under some kind of plasma weapon than an actual laser. I.e., the humans fired back with lasers in that same flashback. And even in that case the "explosion" was simply the super heated plasma expanding on contact and creating a crack/pop. Not something I would imagine as an actual explosion, per se.
Why wouldn't lasers simply have tons of pierce?
That is about as incredibly wrong as anything you could have ever possibly said. Any time you dump a large amount of any kind of energy into a small area in a short period of time, you get an explosion. And yes, this includes thermal energy. This is a pulse laser. It has a fire time of one millisecond, and a high yield. If you put 300,000 joules onto a circle one centimetre in diametre in a time that short, you will get an explosion with roughly the same force of a small grenade.