The CLI is easier to integrate into a normal development workflow, than clicking buttons, dragging files, or copy/pasting code to get the code into the browser.
I guess this supposes that "normal" means somewhere near the command-line, which might not be true for all developers.
> I can't think of a single manager that I've worked for who would accept me saying, "it's going to take me 3-6 months of refactoring & building tests before I can start fixing bugs and providing enhancements."
I can't think of a single developer I've worked with who would try that approach.
When a bug is identified in a project with few-or-no tests, the approach that I usually see taken is to write some sort of large, slow integration test that exercises bug, then fix that. That allows you to prove that the bug exists and prove that the fix fixes it, at least for the documented case(s).
There's no reason to cover an entire legacy code base with tests if you're only changing a small portion of it.
I guess this supposes that "normal" means somewhere near the command-line, which might not be true for all developers.