The scoop: Scheme and Janet are great, but the author wants a more standalone language. What makes the difference is the breakloop, a full-blown REPL that opens when an error in a program occurs. Not a stacktrace, not a debugger; just build from the point where it's currently broken.
This sounds so amazing, why is Common Lisp not the most popular language out there? (asking as someone who almost never writes code)
there is no full-featured web framework (although you can write web apps of course),
no satisfactory GUI lib (now Gtk4, Qt5 (hard to install), IUP, nice-looking Tk themes, more low-level bindings to graphics libraries etc)
the package manager came late,
good open-source compilers came late,
less choice in editors (now many https://lispcookbook.github.io/cl-cookbook/editor-support.ht...),
and, well, lots of FUD and a language not for everyone.