I think your right, in some ways, it's like a symbiotic partnership. You want a supervisor that's well known in the field so that means more chances of making good contacts. One that has had many happy phd students (completed) means they should be a good, supportive supervisor. You hopefully want to publish and attend and present at conferences.
Your supervisor wants a good student that wont show them up. It's also like when parent's say, my son/daughter is doing such and such. They will want to make sure you get some publications which means more for them. Any presentations you do at conferences, again their name is mentioned and the research group is promoted.
When supervisor's can't be bothered, like you say, it makes no sense. They are trying to ruin this two-way beneficial relationship.