> Imo in Ruby it's not that common that service calls are deeply nested. In frontend it's opposite. Components are very nested

This feels like the answer that makes the most-ish sense, although I've worked with a ton of nested Ruby code as well.

My suspicion on why people use Typscript is that it's is more about the tooling than types. In Ruby or Python, I can drop into a REPL anywhere in the code and be in context of what I'm trying to do, but that seems way less common in Javascript. Perhaps because of the async nature?