It made sense that composers pretty much all wrote their own software or built their own circuits in the early days. Part of your individual identity as a creative artist is that your individual working methods and working set-up are highly personal and individual. It would have seemed absurd in those days to expect another person, especially a group of people not musicians and who didn’t even know you or your music, to configure a computer or synth for you. Such work was an integral part of the composing process. I find it has a very stiff and somewhat off-putting feeling by comparison, working now with fixed pre-written off-the-shelf software or hardware units. The music you’d find in an early technology would lead you to modify that technology to make it easier for the kind of music you found in it to emerge. So their was a back-and-forth. You’d evolve both the music and the tools so they worked best together on a specific piece. The music was always influencing me to alter the technology to serve it better, and conversely, the technology would suggest things to try and lead me to new places in the music.
from Interview with Laurie Spiegel at Tokafi.
Also worth reading this interview from the New Yorker, promoting the reissue of The Expanding Universe LP.