The owner could personally evict them.
Yes you would think so... should be easy to get them out. We have friends whose elderly parents lived in Seattle. A broken down RV parked in the alley behind their house. After a few days they complained but the police said that there was nothing that they could do. Their RV's toilet either did not work or their tank was full because the people pooped in their back yard every day.
The elderly parents could not get any sleep because the squatters were loud as well and they were so worried and irritated about the situation. Their dad had a stroke at least partially related to the stress of the situation, and he died a few weeks later. The mom was afraid to live alone in the house. As soon as she stopped staying there the squatters moved in. The police would do nothing about it. It took months and thousands of dollars for the eviction process to complete. When the squatters finally left they had stolen everything and trashed the house to the point that it was condemned. The house was torn down and their mother died as well.
Nothing happened to the squatters and I assume that they went on to another place and did the same thing.