Yeti is appealing to people for the following reasons (and I'm making yeti male for ease-of-reading):
1) He's human-shaped.
- It wouldn't work if he wasn't. We wouldn't relate to him. He's an extension/projection of us anyway.
2) He's ape-like and covered in fur.
- He can't be too human. Fur is a nice obvious simple touch. It makes him still a mammal. A creature covered in scales is a little bit too other.
3) He's naked out in the frozen wastes.
- We admire his clear superhuman ability (and nudist freedoms).
4) He has the option of being monstrous.
- We like that he might be mean and beastly and primal, killing yak and human adventurers with abandonment. But he doesn't have to be. He could just as likely invite you to his cave to share the warmth of a fire or hug a child. But it's nice that he can be both.
5) He's usually alone.
- Free from society, the man-beast has a lot less worries.
