The problem is that it’s a bit illogical. A bigger explosion radius sounds good and useful, but it’s the opposite. The exact details you can find on the Uni wiki listed above but here’s the simple explanation:
If a target isn’t big enough to get the full explosion radius of a missile, the damage will be reduced. So if the target is only half of the size of the explosion radius, it’ll only receive half the damage.
So “paper dps” (what is stated in the fitting window) doesn’t neccesarily mean much. In cases where you have different size targets, frigates, dessies, cruiser, BC and possibly BS (so missions), damage application modules become massively important. Guidance computers and enhancers, rigor rigs and possibly painters if you really are a masochist.
Similarly explosion velocity: if the target moves faster than the explosion velocity of the missile, the applied damage is reduced. Explosion velocity is less of an important factor than explosion radius but it still matters, To help that there’s the same guidance computers and enhancers and Flare rigs in this case. Painters don’t help with this.
This all means that a PVE ship fit that uses heavy missiles or bigger that doesn't have damage application modules is thus a crap fit that loses massive amounts of applied dps. It takes MUCH longer to kill and thus complete the mission. And guidance computers or enhancers are the preferred method, that or rigor/flare rigs.