Maybe because of that inconvenient "equal protection of the law" thing.
Would that it were so. The police are under no specific obligation to protect you individually, btw. So you can't sue them if they don't do their jobs. Most officers do their darndest in a tough situation IMHO, but it would be much better if the judges of this country had to make do JUST LIKE THE REST OF US and no special privileges for them. Then maybe they would have a better understanding of what the 2nd Amendment means.