It's because not every situation is clear cut and they want to err on the side of not making people homeless. How do you know that someone is squatting and wasn't just given permission to live there for free but now the property owner changed their mind and wants them gone? Even if you aren't paying anything, you are still a tenant if you were allowed to live there. They can't just kick you out like that with no notice. Since there is no way of knowing who is telling the truth, they just say "evict them like a normal tenant" so you aren't potentially making someone homeless when they had the right to be there. Unfortunately people take advantage of this and just illegally squat without ever having permission to be there in the first place but homelessness is much worse than having to evict someone.