> what's the deal with calling depth thickness

It's almost as though the author thought about and cared about the content and exact words he chose. "Thick or Treat" and "Thickening agents" and "Slim pickings" even immediately evoking imagery of a thin slop gruel in my own head.

By using an unexpected word I think I thought more critically about it, in fact. Had the author used depth I would've immediately had more superficial imagery in my own head.