I don't think it's lock-in or billable hours. I think "staying current and employable" is a much bigger influence on behaviour than either of those. Also, I th

I don't think it's lock-in or billable hours. I think "staying current and employable" is a much bigger influence on behaviour than either of those. Also, I think most developers just don't want to do the same thing twice. And most developers really are writing the same software over and over again through their careers, with minor changes. So they need to change something to keep it interesting, and the only things they can easily change are technology and methodology.