Why did life not evolve to use radio?
There is a very different mechanism for generation (and detection) of ultraviolet, visible and infrared light vs radio waves.

For the first, it is possible to generate it using chemical reactions (that is, chemiluminescence, bioluminescence) with a typical energy of order of 2 eV (electronovolts). Also, it is easy to detect with similar means - coupling to a bond (e.g. using opsins).

For much longer electromagnetic waves, and much lower energies per photon, such mechanism does not work. There are two reasons:


typical energy levels for molecules (but it can be worked around),
thermal noise has energies (0.025 eV) which are higher than radio wave photon energies (&lt;0.001 eV) (it rules out both controlled creation and detection using molecules).


In other words - radiation which is less energetic than thermal radiation (far infrared) is not suitable for communication using molecular mechanisms, as thermal noise jams transmission (making the sender firing at random and making the receiver being blind by noise way stronger than the signal).  

However, one can both transmit, and detect it, using wires. In principle it is possible; however, without good conductors (like metals, not - salt solutions) it is not an easy task (not impossible though).