I had the exact opposite reaction - allowing me to play songs for free let me experience the service, so by the time they asked me to sign up I was happy to.
If I'd been able to listen for longer than 10 minutes so I could get a feel for how well the selected songs match with what I want to hear, I would be too. But they're not the only service out there offering free music, and besides, "free" isn't enough to entice me to do anything anymore. I get into my local movie theater for free because I'm friends with their their HR manager. I never use it.