I think the killers were probably in the house when the Shermans came home. Given the neighborhood, the perps probably believed there was one or more safes in the house. So they may have hurt the Shermans to find the locations of any safes.
Burglary is a very serious crime, and interrupted burglaries can turn into horrific crime scenes. Adrenaline, and poor/no impulse control jmo.
I had read early on here that there had been several burglaries in that area , in the time before the Shermans' murder.
The burglaries you refer to were in a different neighbourhood, the Bridlle Path.
The Shermans did NOT live in the Bridle Path area.
I don't think this was a bungled burglary. It was a targeted double murder. Nothing else.