Chickadees don't sit and eat at bird feeders.....they typically grab one seed and then fly to a nearby branch or perch and eat the seed there and then return to the feeder for another one. Rinse and repeat.
Titmice and nuthatches behave the same way. We have a ton of them that come to my feeders....prob seen 6-8 chickadees at once before near the feeders but typically not all on the feeder at the same time as they are in different stages of flying to and from the feeder after grabbing a seed.
Years ago, I read one theory on why those types of bird do that and it was because their beaks aren't strong enough to crack open sunflower husks, so they need to peck at it while holding it down on a branch to open it. Finches, grosbeaks, cardinals, etc all have much stronger beaks that can crack open the sunflower in one shot.