Markdown took over because GitHub decided it should, instead of picking ASCIIDoc which is a better format, has a standard, and is literally used by the git documentation itself.

I argee. Up until now, the most PITA for me in Markdown is the table syntax. Even CommonMark does not have any spec for table except for long running discussions with lots of proposals.

AsciiDoc(tor) has a nice support for tables. It also supports more complex features like merged cells, span cols and all but the syntax suffers from there. I guess that is also why AsciiDoc was not widely adopted.