I think I may have found the explanation, or one that fits the facts:
see
https://www.cpsc.gov/Newsroom/News-Releases/2021/CPSC-Issues-Consumer-Safety-Warning-Serious-Injury-or-Death-Can-Occur-if-Lithium-Ion-Battery-Cells-Are-Separated-from-Battery-P...
I came to this thread after looking for 18650 batteries on ebay and
seeing only a few listings, but lots of listings for larger and smaller
form factors. I couldn't imagine why the most popular form factor would
be missing while leaving the rest, so ...
