Well, for one thing, conventional analog broadcasts have not ceased. For example, every FM radio station in North America still broadcasts using the old fashion

Well, for one thing, conventional analog broadcasts have not ceased. For example, every FM radio station in North America still broadcasts using the old fashioned FM carrier approach with stereo multiplexed on an AM subcarrier. So-called "digital" stations in North America use OFDM sub-carriers stuffed into the band edges (HD Radio), but they are still backwards-compatible with analog radios due to the widespread deployment of the existing technology. Also, amateur radio does not necessarily mean old-fashioned and analog. There is a lot of work by amateurs into Shannon-approaching communications on the HF bands, for example. The ham bands exist primarily for education and experimentation. Backwards compatibility is important. Education is important. Filling the bands with spread-spectrum Shannon-approaching noise may be optimal as far as maximizing data throughput is concerned, but it does not serve some of the other practical constraints on spectrum use.