/ic/ - Artwork/Critique

I don't know the inner workings of being a professional mangaka, so bear with me. Why do most professional manga artists find themselves in a situation where they are struggling to hit deadlines on their next chapters? What's stopping them from creating the entire manga from start to finish, and THEN go into the field and drop the chapters weekly or monthly without having to worry about meeting deadlines?

I want to create a manga one day, but I don't want to have to worry about deadlines, especially because I'm really lazy and have no drive to draw every day, I just want a create a story and share it with the world, so I was thinking I could create the entire thing first, and then release chapters every week or month safely.