Someone hinted at this already but could the interior of the hen house be too warm? That might be one reason.
We moved our chicks out to the coop at 5 weeks, but did not let them out of the coop until just now at 3 months (12 weeks). They did not go into the hen house on their own at first and we would carry them in and shut the door. After about a week, they began putting themselves to bed in the hen house.
Now at 3 months, we let them out - they foraged for a few hours and then walked themselves right back into the coop. Maybe keeping them in the coop for awhile and not giving them any other options will help? I'm new to this, too, so I'm not certain about this...
Do you have enough ventilation in the coop for you poultry this can be a problem at times and poultry do like to have ventilation as much as you do so even a large window fan can make a lot of difference as my poultry were roosting on the front porch for some time and now like to roost on the swamp coolers silly birds but with putting in some window fans to move the air around a lot more of them are roosting it there where they belong .......
I had to cover everything up to keep thing clean ....