I'm an amateur radio operator, and though I don't have direct experience with remote antennas for drone controllers, I may be able to shed some light on why you don't hear much about them.
Antennas are normally connected to radios via coaxial cable. The cable always has some loss. The loss gets worse as the frequency gets higher. It also gets worse as the cable gets longer.
RG-58 is a popular coax cable for general purposes. As an example, assume we need 30 feet of it between our radio and rooftop antenna. At CB frequencies of 27 MHz, that results in a loss of about 0.6dB, meaning that 4 watts of transmitter power at the radio results in 3.5 watts of power reaching the antenna, not a bad situation.
But that same 30 feet of RG-58 at 5.8 GHz (common frequency for our remote controls) results in over 17dB of loss, meaning that the same 4 watts of transmitter power would result in 0.076 watts of power delivered to the antenna, with the rest of the power lost in the coax.
At the frequencies our remote controls use, for reasonable lengths of reasonable coax, almost none of the power reaches the antenna. The situation is similar for reception: almost none of the received signal makes it from the antenna to the receiver.
The problem can be mitigated by amplifiers at the antenna, but since the receiving amplifier is amplifying in the opposite direction from the transmitting amplifier, there needs to be some coordination to switch one on and the other off at the right time. It would be very difficult to get this to work unless the RC were designed with a remote antenna in mind.
Here's a calculator to run other scenarios.
Coax Calculator
