From what I understand the four major hurdles for moving from OTA broadcasting to streaming are:
1. Cost to consumer. Granted this means more to some than others, but streaming via the Internet is basically a subscription model. A larger number of listeners than you might imagine, are used to free radio. Internet bandwidth costs money, even if baked into your smartphone plan. In spite of AM listeners aging-out, how many would be willing to pay or even understand the technical requirements to receive a streamed radio station in their home or car when used to it for free? That is one of the business limiting barriers that SiriusXM (satellite radio) ran into and still hasn't resolved.
2. Community-based radio stations get lost in the Internet radio streaming ocean. Thousands of well intentioned people starting streams all the time, only to fail because they don't have the marketing capital to stand out and retain listeners. Take a popular syndicated talk show currently on AM for example.. Why would a listener in Seattle go specifically to that local station' stream, when there are a sea of other choices available? Ultimately the local station loses, big time. For AM, estimates say plan on losing 80% of your existing audience.
3. Geographically controlling the stream. "Geo-Blocking" a stream to include only the coverage area of a market is possible, but it comes at an additional cost along with the stream. For various reasons, advertisers and agencies can't allow spots developed for local or regional stations to go outside that region.
4. SoundExchange, etc. Currently OTA radio stations are given consideration when it comes to licensing and royalties. Lose the OTA component, and costs go through the roof (by comparison). One of the many reasons that "popular" streaming services like Pandora haven't made a red cent of profit to date. Why do you think Pandora went out an bought a radio station?