Why is 长 never translated with 'look like'?
It's true; a lot of sources don't mention looks. I'm not sure why. But, here is one that does:

Wiktionary


  (of a person) to look; to appear (e.g. beautiful)


Also if you have Pleco, you can check out Tuttle, their definition includes:


  grow to be, look


A lot of resources are more likely to put this definition under 长得.

MDBG


  to look (pretty, the same etc)


This is likely to be because you'd be hard-pressed to find 长 by itself talking about looks with a 得.