I think the key to giving out free passes is to make it rare. Also, if I set some nominal price, even $5, then people are likely to decide for sure they want to go and how many. I also had to explain to them that just because the tickets are free, that does not mean you can act like it's a picnic, show up late, talk, eat in the theater, leave early. If anything, you should be on your best behavior. I finally decided I would only give out tickets to people who had earned it by going to smaller brand theaters, even free, and showed they understood the etiquette. Plus there's so much on the internet now. Do you sit down and listen to a 45 minute symphony at home, then you get to graduate to the live event. Are you bored after ten minutes of Giselle, then a live version probably isn't going to hold your attention either.
By and large, I would say a lot of people just wanted to be able to say they had gone, kind of like bragging about overseas travel.