According to Puddin' Man Pudding Dot Man At Gmail Dot Com:

It came with a single-gang box with a standard 2-position switch to
control a ceiling fan/light assembly.

Whilst replacing the switch, I noted the usual red and black wires.
One of the black wires was stripped about 1 " in the middle (where
the wire was not cut), kinked, and wire-nutted (nothing else in the
nut, just the kink). Both the strip and the wire nut serve no
purpose whatsoever that I can see.

Has anyone seen anything like this? If so, know why they did it?
Near all the old wiring in this tiny house is extremely simple
and predictable: worries po' me when I see something I can't
explain.

Another possibility:

At some point there may have been a combined switch/outlet device
(or a double switch), and that bare segment was a connection to the
outlet. Then, they replaced the device with a simple switch, and
needed to protect the bare spot.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.