It is a measure of how screwed up our legal system is that this wasn't the default position of the entire legal system.
Yes, the owner should have the right to eject anyone who doesn't belong there.
It kind of is.
But the police do not want to do it. So they go, "it is a civil matter now our donuts are getting cold so go away."
In fact if you dig a little into the law, and not very far, you find that indeed they can do something.
If you go to the media with chapter and verse about how they can do something (do not expect the media to do ANY research) and manage to get them on a slow news day and you have a bad enough "trauma story" you might be able to get them off their steadily expanding butts to do what was their job all along. Once upon a time when the organized police force in NYC was a new thing (and run by the Irish) you had to offer a "reward" to have a crime "solved". And by "solved" I mean they picked out some poor blighter and beat the bejabbers out of him until he confessed.
This was somewhat changed when Teddy Roosevelt became the police commissioner but as the twig is bent.