This is a somewhat soft question, and I'm far from an expert on the subject, so it's possible that my premise is factually incorrect.
The practical generation mechanisms for useful real-world coherent EM signals (e.g. for wireless communication, radar/lidar, etc.) seem to be very different for radio vs. visible signals.
From what I can tell, radio transmissions tend to be generated by AC-driven antennas, which are naturally isotropic in at least one plane through the transmitter. While it's possible to generate a directional beam at radio frequencies, it's much harder to do and requires designing an antenna array in which each element is individually driven with a separate carefully controlled phase offset.
On the other hand, coherent visible light seems to be typically generated by lasers, which are naturally highly directional and narrow-beam. While there may be a way to generate an isotropic coherent visible-frequency signal, it seems much harder. (It is of course easy to generate an isotropic incoherent visible signal; just turn a light bulb on and off.)
It seems to me that purely mathematically, it's just as easy to construct a directional coherent RF signal or an isotropic coherent visible signal as the opposites. The difference between radio and visible frequencies seems to be only quantitative in theory, but qualitative in practice.
Am I correct that it's practically much easier to produce an isotropic coherent radio-frequency signal than a directional one, but conversely it's much easier to produce a directional coherent visible-frequency signal than an isotropic one?
If this is correct, what is the fundamental reason for this opposite behavior at different frequencies? Is it simply due to the nature of the currently practical generation mechanisms, or is there some fundamental reason intrinsic to the EM waves themselves at different frequencies?
If the former, is there a fundamental reason for the huge difference between the practical transmission mechanisms?