No, they are not required to play covers, but as you say, the audience likes you much better if you do. Which proves the point that you and the band are making your money off of those songs, the rights to which belong to someone else. So you pay a fee. You don't like it? Just hire all original bands, like U2. Plenty of punk bands, which is how U2 started, play all originals. But something tells me that might not be good for business. So drop the pose that you are really just an overcharged patron of the arts. That's BS, and I've proven it.