Making * always be used for bold and _ always for italicizing is so much clearer, and some Markdown flavors (notably WhatsApp) do this. So you only have to do *haha* or _haha_, which also makes italic-bold more _*intuitive*_.
Similarly they should have gone with one style of headings, probably with #.
This frees up more visual clarity. Because you are no longer using *** for bold-italic, you can use that for lines, instead of both --- and ***.
This then further frees --- up to be used for tables.
Although I imagine there's a decent subset of people that uses the alternate style of doing headings === and the 'normal' way of doing lines ---, which would have killed adoption.
And good luck convincing people to adopt a new variant at this point. "Commonermark"? "Peasantmark"? "Rabblemark" actually sounds decent.
Edit: actually, having checked the discourse around it a bit more, Commonmark wasn't created as "one Markdown to rule them all", but rather as "Venn diagram markdown with the most overlap".