It shouldn't take any development time, but the app stores are all run on over-caffeinated ferret logic, so yeah, they do need to have someone update.

Keeping things updated is like a week of work for one junior developer every few years. A small team could do it for a large company's apps in perpetuity. But under the ideology of capitalist software management, keeping such a team around is functionally impossible. (They would have idle time, some manager would see that and give them extra work, then when the app updating job picked back up, that manager would convince everyone that the other work they were doing is more important than updating apps.)