i can see your point in smaller departments.
in my experience, it doesn't pay to "trump up" charges. too many checks along the way. you have to call a boss to the scene in order to verify the arrest. they can tell you to cut the guy loose or write and summonse and let him go at the scene.
if you do arrest, then you have to draw it up with the ADA who can decline prosecution right out of the box over the phone.
and you don't want a reputation as someone who can't handle a situation and has to arrest everyone who gives you attitude.
Yeah, where there is evidence, cameras, witnesses, paper trails etc...However, in many incidents, it's only the LEOs word against the suspects, and all rides on who appears more credible in court. It's easy to "embellish" events or incidents, for both the suspects, and LEOs.