Yes there is an explanation for this

In order to hear the controller, it would require the receiving radio to be very close to the transmission site that is located on the ground. On the other hand, the aircraft are transmitting high in the sky so their signals will travel much much farther than a controller's transmissions from the ground. When a feed site is not close to an ATC transmission site, you will only hear the aircraft in the sky.
Sometimes a controller will switch to an alternate transmission site which might not be in range of the feed site.
I hope this makes sense

Ron