I was thinking the same thing. I think someone was in that area for a different purpose and saw Abby and Libby, and it became a crime of opportunity. LE have indicated that it was "all over" very quickly, which makes it seem that BG was looking to kill someone, not sexually assault them. I've often wondered if it was somehow connected with someone visiting the nearby cemetery. I've looked through the gravestones, looking for someone who died in either later January or early February, thinking maybe someone was making a visit to a relative.
I spent a lot of time reading at the cemetery online. One person stuck out as a repeat visitor to the cemetery that had children and a spouse that was into drones. The spouse died a few months before the murders.