Because each police agency chooses their own police officers from their own hiring pool of applicants. Every state and jurisdiction has their own hiring criteria (ie: education, training, background issues, ethnicity, training standards, etc.). What might be acceptable in one part of the country might not be in another. Some agencies prefer their officers to have higher levels of education and are willing to pay higher salaries to get that type of candidate. Other agencies want lateral transfers because they can't afford to send folks through a basic police academy. In general you really get what you pay for with regard to police candidates. The more tightly you screen them and the more education you require them to have (or get while employed) and the cleaner their backgrounds, the better product you start with going into a basic police academy. Every individual going into law enforcement brings things with them (ie: prejudices, like/dislikes, experiences, etc.) so each person is unique and so is their technique of enforcing the law.
You can try to spin it all you want. No one should point a weapon to the crowd and threaten to kill them. Rember, police are not the law or above the law. Police are hired to enforce the law. They often break the oath the swear to uphold.
