There had been an interview with a witness who said that officers were at the scene telling people to evacuate. The response time could not have been very long, and an Orlando Officer took down the suspect.
From reports, the incident began around 0200 and the police breached the building around 0515. They did have reports of a bomb vest, and were probably at a loss as to how to respond. Suicide bombers tend to leave slim pickins in the rational response department.