Later on, he developed an okay drop shot. Not at the time of Segura's comments, though. If you look at the 81 Wimbledon semi, he uses it against Borg a few times. Not a ton. 5-6 times? Ashe was sort of working with Connors at the time. He was real big on the idea of needing to draw Borg in. Talked about in OFF THE COURT a bit. I mean Connors specifically, that Borg was just too good at the baseline.
Thing is, Borg was so fast that it better be a good drop shot. Also, Ashe was probably thinking that even if he was a very good volleyer by that point, he still wasn't as good as he was from the baseline.
Good point about Borg and drop shots. Offhand, I don't recall seeing him try any.