I think Leonard was staying out of the way and far too cute to get mixed up in the excruciating 'jam session' on live tv with out-of-tune guitars and even more so out-of-tune voices

My guess is that if he had picked up his guitar and started singing something like Crazy to Love You he would have made them all look like the load of old has-beens they are (unlike Leonard who is cool to the core).
Paul Simon droned on as usual, and it's a long time since anything worth listening to came out of Keith Richards's mouth even when we could still understand him. I would usually feel sorry for somebody who is hard-of-hearing but I think Chuck was the lucky one not being able to hear what was going on.
I take nothing away from any of them as songwriters, over the years I have listened to and enjoyed a lot of their music and lyrics (Elvis who?) but none of them has even come near to the heights that Leonard achieved lyrically. In my opinion he is just on a different level altogether - a "hundred floors" above them.
Evie B