No, just experience with a lot of codebases.

Here's a simple question to ask yourself: what if non-IO operations allowed you to use the .then() syntax? If you have the choice to use:

   1 + 1.then(function(result) { ... }

vs

   const result = 1 + 1

Which would you choose?

Using then() doesn't pause execution of the callsite function, while await does. Surely that's a relevant difference here?

It doesn't seem unreasonable to use then() to express: "Run this anonymous function whenever the async thing completes. Meanwhile let's do this other stuff right now."