All other electronic instruments, with the one exception being the Theramin, have a fundamental problem with human expression. There is an unsolvable disconnect between what the performer's actions and their audience.
See: https://www.scribd.com/document/55134776/48787070-Bob-Ostert...
With an electric guitar you get the physicality and dynamism of an acoustic instrument with the complex timbres and extended technique possibilities of an electric/electronic instrument.
There are complex and musically significant feedback loops occurring across many dimensions that lead to extremely complex transformations of timbre via both traditional music theoretical techniques and the physics of a tube amplifier combined with an inductive load (the guitar pickup).
Its really crazy how much more dynamic and complex this can be then even a highly sophisticated modular synthesizer or whatever. Even the way you over load the power supply in a tube amplifier can be manipulated on the fly to enhance and transform timbre.
Then on top of all that it is so incredibly physical that a performer like Jimi Hendrix can manipulate these systems and have the audience intuitively understand what he is doing. Never in a million years would THAT be possible with any other electronic instrument.