Skyrim’s followers have a maximum carry weight and won’t let you trade them any items after they exceed it. That is, if you TRADE them the items! You can just Hold E/talk to them and go into interaction mode and order them to pick up things from the ground. They will happily do so without complains regardless of their carry weight status, extremely helpful for collecting a bunch of dwemer junk to smelt down into ingots for smithing - those things are heavy!