It was briefly renamed Common Markdown as well, and John hated on that as well, so it became CommonMark.
And now we're in an odd position where Github and friends all validate their implementations against the CommonMark suites, but refer to the result as "Markdown" to their users, which makes the work they're doing maintaining that stuff especially thankless.
And then there is GFM (Github Flavoured Markdown), which is a bit different from Common Mark.
At the time of the SM/CM/CommonMark kerfuffle a decade ago, Gruber was quite explicit that "X Flavored Markdown" was perfectly fine with him— Atwood even includes the relevant podcast snippet:
https://blog.codinghorror.com/standard-markdown-is-now-commo...
Honestly the whole thing is so ridiculous.