I think it's just that there aren't as many ice types in Gen1/2 as fire. The only not-uncommon things on the ice side of this event (here anyway) are Swinub and Shellder, and the latter only gets ice on evolution. Less common, there's Seel and Sneasel, and evos of the first three, and then Jynx and Lapras which are still pretty dang rare. I think that's about it?

Whereas fire you've got Growlithe, Ponyta, Vulpix, Houndour, Charmander, Cyndaquil, rarely Magmar and Flareon, and all their evolutions.

Too bad the couldn't sneak in the Alola versions of Sandshrew and Vulpix, that'd give us some more ice. ;)