People can get proprietary software for free too, if they don't mind pirating it. It might be illegal and the risk of getting malware increases, but many people do it anyway. Sometimes it's even better than the original, because the pirated version won't have DRM.

So in practice nobody has to pay for any software, any movie, etc. People just choose to do it. In case of Free Software getting it for free is just easier and safer. In theory this might mean that there is less incentive to pay for it, but some projects that I've seen seem to be successful. Maybe people don't know they can get it for free, or it's too much effort, or they are simply fine with paying.