Do you have any explanation why Karoli did not do solos ?
Again - another interesting question. Because Karoli was a bit before my time, I had to look up some of the history behind Can and Karoli's background. My knee jerk reaction to doing solos is that if you had no interest doing solos at all, ever, you probably felt that song/music as-is is strong enough to stand alone on its own, it doesn't need to be "highlighted" nor does it need that mood enhancements when it comes to experiencing a solo in relation to the music's story/emotional connection.
As it turns out, Karoli did not believe in pre-arranged music, and would often perform in a "just get up there and jam", playing off the other's reactions at a given moment in a very dynamic and reactive way. Performing improv style this way imbues a sense of having a unique solo each and every time. It seems Michael reveled in that process rather than being encumbered to performing a static set of notes time in and time out.
So finding this out (from the article below) I can understand his not having a need to perform a "solo" in the traditional sense when each performance in and of itself becomes a version of a unique solo in his mind.
http://www.muzines.co.uk/articles/michael-karoli-on-guitar-improvisation/5919