They aim to standardize the "markdown-like" formats into a single unified one. It's not done yet but it's certainly better than everyone for themselves.
Does anyone remember Creole wiki markup? It was born in a time when each wiki created its own syntax. Creole should become the standard for wikis, but it never got traction. I fear that it will be the same with commonmark.
This kind of reminds me of the XKCD[0] Standards comic strip. I love writing initial documentation in Markdown because I basically just punch out a text file with line breaks separating my sections/headers and add in some of the markup quickly after I get my content written.
It really is annoying though when I have to be careful about a convention that I'm using if I'm putting a README in BitBucket vs GitHub vs whatever else. Generally, if I'm just sticking to headers, lists, and quotes, I have no problem and everything works and I don't pay it another thought.