Tv uses a _lot_ more bandwidth than radio. The analogue tv spectrum gets repurposed for 3g/4g etc, but the frequency of FM radio doesn't provide remotely enough

Tv uses a _lot_ more bandwidth than radio. The analogue tv spectrum gets repurposed for 3g/4g etc, but the frequency of FM radio doesn't provide remotely enough capacity to be able to justify it for this reason (though there are other reasons, such as being able to have to have overlapping transmission towers)