I'm gonna post something that I know is not going to be received well by many. Before I do, please, please note that I am heartsick for those who have lost a Dad, Mom, brother, sister, son or daughter. And I am certainly supportive of the job that most LEO perform, under less than ideal circumstances. But: This should not have happened. No way that four LEO should have been taken this easily.
I spent some years riding in a motorcycle club (not any longer). Due to the nature of that subculture, we were ALWAYS on alert. If 4 of us went into a cafe, we did not all sit together. At least one positioned himself well away from the group in order to watch the surroundings. It would have been very difficult for a single person with a semi-automatic handgun to take out the whole group. Not impossible, nothing is impossible, but very, very difficult. Always we did this, no exceptions.
( Before anyone gets too excited or starts to stereotype, the club I was in engaged in no illegal activity and there were many vets and other patriots who rode in the club. The fact that there was a patch on your back, however, made you a target.)
So, I tend to ask why a group of LEO does not conduct itself the same way. Certainly, many LEO on this site have posted about the well-armed sociopaths who exist in our society. Why would any LEO not consider themselves as targets and conduct themselves accordingly? Arrogance, complacency? I don't know...
I realize I wasn't there and it's often difficult and foolish to second guess exactly what the circumstances were. I also know that if someone targets you, it's difficult to impossible to defend against, at least one-on-one. So, I'm not fault-finding here, just opining for sake of discussion.