2 Cent Theory
Both bodies were "hidden" in a back bedroom because they were being extra cautious, not wanting to take the chance of bodies being seen too early. Not only did they want to finish what they started but they needed time to get rid of all those security cameras (maybe phones if they stole them) and the guns, brass catchers, bug detector, shoes, masks, all their clothes etc...all those murder kit purchases.
If someone went to Chris's too early and the door was unlocked they could go right in then be calling 911, way before the Wagners were ready for that.
With the door locked a visitor could assume they are sleeping and not want to wake them, at least not until BJM showed up around 7:00am. The longer it took to get into the houses means the longer it took to call LE.
Note that Frankie and HG were already in the bedroom and their door was locked.
My theory is contingent on Dana's door being locked also.