This is the equivalent of a writer being asked to edit and make changes to the same book every day, into perpetuity, long after they’ve reaped the initial financial and reputational rewards from its creation. What’s more, unlike other content, open source code is relied upon by people, companies, and other institutions that need it to keep working, long after the maintainer’s interest has waned. External contributions don’t necessarily reduce the burden of maintenance either, because they still require someone to review and merge them.