(vs Normal AI)
(And it was an exercise in futility anyway--the region was one of the linking ones without resources of it's own and I owned all the downstream regions it linked to. The AI shouldn't waste orbitals on defending a region that isn't currently useful.)
I think from the AI's perspective (And frankly, even mine more often than not), it's better to do the fighting in a region where collateral damage is irrelevant, than to let it progress to your own base, and to let the opposition collect territory unopposed. Obviously in this particular instance, things didn't exactly go as planned (With it registering your artillery as a ground-attack), but the base logic of "throw tons of quanta at a resourceless node about to fall" makes sense.