It is very easy to prove if you get called to the stand and don't show.

That isn't obstruction of justice. That is just failure to follow a court order. Obstruction of justice requires the specific intent to hinder the prosecution and requires some kind of affirmative action to do so, i.e. lying. Simply not showing up to court isn't going to cut it.

The reason it doesn't happen often is more to do with the relationship between the DA and the police. If the DA starts prosecuting officers in accordance with the actual law, the police are going to become uncooperative with that DA. And as how an investigation is handled impacts the case this could fuck the DAs conviction rate, and therefore their career. We need to change the system so the people who prosecute police accountability cases are not the DAs.

Police already cooperate minimally. It isn't like you see on tv. Most prosecutors can work their entire careers and never significantly interact with a police officer outside of a court room.

We need to change the system so the people who prosecute police accountability cases are not the DAs.

We do, most of the time it is the Attorney General.