Radio is free to the listener, but it isn't costless either. It's not free to the broadcaster (both because of the limited range of frequencies requires renting a frequency and because the infrastructure needed to broadcast costs money). I suppose the future you imagine is close to free, although it will still cost the price of the equipment to broadcast (and the electricity to power it).
If the question is about making the internet costless to the consumer, there needs to be a viable mass-use revenue source for people like commercials are for radio. This would have to be on top of the revenue sources for individual websites. Things in the past like pay per impression ads generally have not been the solution.