Because he was deemed to be acting reasonably. That reflects more on societal issues than the policeman himself.

The people who would be responsible for prosecuting the officers are the same people who prosecute everyone else in that jurisdiction. Through all those other prosecutions, they tend to develop a strong working relationship with the police force and are typically on the "same side." It's also very rare for police to testify against their colleagues — as you might imagine.

That's not the only reason, nor is it always the case, but it's one of the big ones.

The US police system has, and expects, a high degree of police militarisation.

It's simple expected that, in the case of a report of violence, weapons, or drugs, that the police department will dispatch a large group of very heavily armed people many (or all) of whom will not be wearing obvious police uniforms, who will proceed to storm the building, often at night, using battering rams, sometimes flash bangs, and at least the threat of overwhelming force. There will usually be some yelling about them being police, but since then happens as the doors are being knocked down, and often while the targets are asleep, this can be easily missed.

These tactics were chosen to make it likely that the targets cannot flee, cannot dispose of or hide evidence, and that those who want to resist the police (standoffs, hostage situations, setting up ambushes, etc.) cannot do so effectively. These tactics are also intended, at least, to reduce the risk of police officers being injured or killed. They were chosen despite the knowledge that it will cause people who would not want to resist the police to do so anyhow out of confusion, and that it will lead to the death or injury of targets, bystanders, and pets.

So in the above story, the SWAT did what the team is designed to do. Why would there be consequences? The point of these units is to respond to reports of violence swiftly and with overwhelming force, which they did. That causes deaths, usually of the targets (or their pets, of their families) but sometimes (as here) of people entirely unrelated to the target. This is accepted by the courts (and more importantly, society) as perfectly fine.

There will be no penalties unless they go way over the bounds of what's accepted. If it comes out the police themselves faked the call, or planted evidence, then that will likely have penalties. But in most cases, mere violence will not.

See, for example, this story: https://www.washingtonpost.com/news/wonk/wp/2017/01/13/india...

Here a SWAT member tossed a flash bang into a room without even looking, it turned out it landed next to a 9 month old infant. That wasn't enough to get him disciplined or anything, but it did get the conviction of the targets quashed, and even that was really unusual and surprising. After all, there was a report of cocaine and a handgun, so obviously a military assault was needed, right?

The officers were acting under the impression the man they saw was an unhinged person who just shot their own father. In this case if you saw them reaching for what could possibly be a firearm many people would likely react in a similar manner. Our survival instincts are incredibly strong.