So I take it you've never shipped an MVP?
This is similar to the responsive/mobile design - if you care about it from the start, you'll structure the site/component in a way that it really won't take you much more time to support accessibility features. If you don't care at all, retrofitting accessibility will require severe refactoring and probably won't ever be done.
So not caring about it in "MVP" is about the worst thing you can do.
You should also keep in mind that you're (implicitly) asking people to do more work – which is fine, but there are real costs and people aren't bad because they haven't already borne them.
Most of my job as a developer is thinking. So yes, it is more work. Accessibility / Responsiveness isn't always done first because it takes more time (either thinking or "working").