Casinos prefer to pack 'em in at full tables. It amazes me how bad business it is for the house to not have every available table game open.
They used to employ shills to drive up action, but in order to cut labor costs they now shut down entire sections.

It's a psychological / social thing where folks don't want to open a new table, but people who otherwise would walk by & not sit down will do so when seeing someone playing. Similar to how they put high limit slots / table games in cut out alcoves & low traffic out-of-the-way areas. Gamblers prefer to sit in dimly lit sections with a feeling of privacy among a few other persons playing a fast-paced game.