I'm pretty sure there are many devs who care about their image inside the community/ies they're developing in/contributing to. it's just human nature to care about stuff like that and not everyone is levelheaded enough to care only about the common goal and the merit for everyone.
also in many cases there's a project founder or a core team that needs to approve your patches if you want to contribute. I bet any new contributor not to confident in their coding skills yet cares about what those people think about them & their work.