Law enforcement officers have a legal obligation to render aid

Even if we accept that point, which is debatable, they have higher priorities. They don't have an officer involved shooting and then the second bullets stop flying everyone just goes into first aid mode.

Securing the scene is a higher priority, even firefighters and EMTs aren't allowed on scene until the scene is secured, so why should some random person who claims to be a doctor? Furthermore the police suddenly become liable for the safety of the individual rendering aid if they allow them on scene.

This entire situation is exasperated by the presence of a hostile crowd, just like the George Floyd situation; had the police not been constantly threatened by an aggressive crowd they could have focused much more on the suspect that required aid.