One of the advantages of intentionally writing a loose, less controlled first draft is that you can put in place basic scaffolding that makes later improvements easier.
They do the work because writing is their job and not just a hobby. No one need ever see that terrible first draft.
Believe it or not you will be able to read your own mess, so if anything slows you down, ditch it and keep running. Instead, they lay out their notes and outlines if they have themand they look for an easy way into their first draft. But in the end, you will be better for it. Fix it later. Keep digging!
What did I learn? Reading dialogue out loud will help you hear better whether your use of it is natural or not, but you can leave this for later drafts. This is also when you decide to push forward and ship your work.
The truth is the most creative, successful people I know are also some of the most disciplined — in their own way.