If it costs the audience something, they're demonstrating their sincerity. So one problem with giving stuff away for free is that you might doubt how much your fans really mean it. Maybe they're just taking free stuff on principle, maybe they're praising you for the pleasure of giving praise, if they don't put their money where their mouth is. Maybe I don't sincerely care about a lot of the free stuff I say I enjoy, it's hard to tell when there's no test of what it's worth to me.

Then again I suppose there's also an opposite sunk-cost effect where a fan feels obliged to insincerely say how great the thing is, because of being literally invested in it.