I’ve never kept them in the brooder that long, but it sounds like pretty normal behavior, especially if your coop is elevated. I usually transition mine at 5 weeks, but even if I leave them locked in the coop for a week they always go to bed on the ground after I let them out. I have to do what you are doing, toss them in the coop at night after it gets dark enough to pretty much just pick them up.
I normally do broods of around 15 to 20 chicks at a time. Sometimes they catch on really quickly and start going to bed on their own, once I only had to do all 16 once and they went in on their own after that. I’ve had some go three weeks before they caught on. What is more normal is that after a couple of nights one or two go in on their own with more each night after that. Usually they are all going in on their own after a week or so. But it can drag out much longer than that.
Sounds normal, but yes it is a pain.