I try not to assume motivation as I can't read minds, let alone hearts, but as a practical matter "refactoring, optimizing, or adding new features" means someone has to maintain something he may not really understand.
Do you mean understand as in "understand the architecture, structure and the domain" of the project worked on? Are you implying working for 5 hours a month only on a project is not enough for these? Is that what you are saying?