The availability of a feed starts with the availability of a volunteer willing to step forward and offer the equipment and time to provide it.
What feed is offered then becomes a matter of reception - what frequencies can a volunteer receive that offer both sides of the communications (not just one side). Most times volunteers are closer to airports then they are the transmitting towers of a center frequency.
However, there may be potential volunteers near center transmitting towers and they just don't know it yet. This is where a bit of investigative work is needed by the community here to determine where center transmitting towers are located.
In the end, I think it simply is a matter of not enough volunteers located near the remote transmitting locations of the center frequencies.
