To each his own I guess. I personally like the HTML-like mental model that HCL gives me. In a sense not being a programming language is to me a benefit. If anything, I'd love to see an equivalent of CSS to Terraform - an idea someone smarter than me was floating not so long ago. Decoupling structure from specifics - I can see a well thought-out implementation of this concept actually taking off.
Re: programming languages... I love programming. Just not my infra.
But a preprocessor that deserves the glory.
Imagine writing in a real programming language, with real variables, loops, function calls, etc. And then imagine trying to use HCL instead.