I think there are "solo programmers", but they either:
1. Tend to have a pretty good memory for their own code so they are comfortable living in their own idiosyncratic world.
2. Don't maintain solo programs for a long time.
Even for group code, I think there is still room for languages that are more focused on "build your own mini-language, then write your program in it" as opposed to "there's one prescribed way to do it".
I think a lot of it comes down to ramp up time. When a new developer (or your future forgetful self) starts hacking on your program, how much time do you want them to spend before they are useful?
Languages like Python, Ruby, and Java try to minimize that by making all code in those languages roughly similar so it's easy to hop from one codebase to another.
Languages like CL and Perl place less of a premium on that. In return, the idea is that once you have ramped up, your overall velocity is higher. You basically have to learn a new language—the "language" that the program itself is written in—but once you have you now can express concepts in that program's domain more succinctly.
I don't think there's a right or wrong here, just different trade-offs to be made.
If there are no solo programmers, then it doesn't make sense to design any part of a language for them :)