I’m unsure why he gave the sled skis instead of repulsors. I mean, sure, it has skis on set, but that’s presumably just so it could be pulled around. I don’t see any greebling on the skis and in universe, it looks like it would use standard speeder technology.
Well, there are vehicles in the SW universe that use both wheels and tank-treads, so I guess he figured why not? Plus, I suppose it could still use repulsors of some kind to propel it.
Also, there’s this exchange between Han and the Deck Officer in ESB explaining why they use Tauntauns;
“Are the speeders ready?”
“Not yet. We’re having some trouble adapting them to the cold.”