It’s a very common mistake. Probably one of those areas where English is just plain odd when compared to others.
I’d like to think of me as being a somewhat competent speaker of English (degree in English, written English heaps better than spoken, I’m sure), but some of these very small quirks are just something I’ve either never learned or hadn’t bothered to remember lol
Many native English speakers don’t know them. To them (myself included) it just doesn’t “sound right” but I couldn’t tell you why it’s wrong.
“like” needs an object for the comparison. Something can’t just “look like”, it has to look like something. “What” is an indirect reference to an object so you can say what it looks like.
“How” is a reference to an adjective or a description, so it doesn’t need another word to make it a comparison. How does the cave look? It looks terrifying.
