I live in Georgia, not in Atlanta but still a pretty busy suburb north of it, so. If that would matter?

If the whole point of this water event is to let players get water pokemon they might not normally get, doesn't it seem weird that some of the fairly-common ones still don't really spawn more with the event?
I went to Charleston a while ago, got one Seel and one Shellder that I figured would sit unevolved forever because I never see them in GA. Then the event gets announced – great! Doubt I'll see a Lapras, but surely I'll get enough of those two!
Sure enough, looooads of Seel, can probably evolve two by the time it ends, and I'm a fairly casual player – have it open at my work desk most of the time in case something pops up.
Also gotten loads of Totodile, decent amount of Squirtle/Poliwag, tons of Azurill, Slowpoke, Magikarp, Chinchou, Wooper, Remoraid, Octillery, etc. Even got a Qwilfish, though no Corsola or the rarer evolved forms of things.

(Tangent - fire event when? Still only at 80 candies for Charmeleon even after starter event, and I've seen maybe three Cyndaquil, but can evolve Venusaur, Blastoise, Meganium and Feraligatr already).

But Shellder? I saw maybe one on nearby the first day of the event, and haven't seen a single one since. I get that there'll still be regional differences to a degree, but for Halloween everything related to the event was out in droves, Valentine was similar (except Chansey, who was about as rare as Lapras), etc.
Why is one fairly-common so hard to find?