I don't know if this has happened to you much, but I usually play slots from time to time and when I get free spins I usually win something, sometimes more, sometimes less, but I always win.
The casinos offering you free spins and bonuses doesn't mean that it's expected of you to win but along the line if you're lucky to have won then it's cool but that notwithstanding I think free spins are meant for the gamblers to express their excitement and enjoy the fun but if you tend to win while doing so it's an added advantage but it's not compulsory that you must win with the free spins.