With the help of my girlfriend and my brother, I've reached the conclusion that the legendary being we refer to as the yeti is not actually a reclusive creature indiginous to the Himalayas and other far-flung cold regions, but an inhabitant of the hollow Earth wearing a sort of climate-controlled environmental suit. Naturally, the hollow Earth is much warmer than the surface, so when any hollow Earth native decides to come out for a ramble, he/she/it needs some protection. The reason that the yeti, as it were, is only seen in certain parts of the world is simple: those places are the terminals of the hollow Earther tunnel network. There are only a few exits to the surface, but there are presumably hundreds, if not thousands, of passages below the surface.

So there you have it.