Because usually a controlled buy is done by a CI who is working off a case of their own. Cops don't want to give up their snitches. If the undercover cop did the buy they usually wait until they've bought as much from as many as the can before they serve the warrants because once the first arrest goes down everyone now knows that guy is a cop.
Apparently their stupid plan went south on them this time. But why kick in the door when they know the home is occupied at all? Wait till they go to the grocery store, bar, where ever. One team nabs them on the street while the other searches the unoccupied dwelling.
Nobody gets shot, well except the dog which seems to be SOP these days, and the arrest gets made.
This no knock crap is getting far too many innocent people killed and injured. They should be reserved for only the most extreme of circumstances.
L