This question is always annoying, but I'll bite:

1. Because Apex processes more flavors of Markdown and seems to have more configurability with regard to Markdown syntaxes.

This is not a knock on pandoc. I love pandoc. I use pandoc every single week day.

2. There is no obligation for you to use it. People can create whatever they want and share it with whomever they want.

Things like Kramdown IALs, for example. Apex can handle a lot of (but not all) of Pandoc's special syntax, including cite-proc and bibliography support, but using Pandoc means you don't get features from Kramdown or mmark. Pandoc is über-powerful, but for 80-90% of simple Markdown->HTML cases, I think Apex is going to offer everything Pandoc does plus the benefit of extensions from processors it doesn't handle, and where it does handle them, you have to choose `--from markdown_mmd` or `--from gfm` --- with Apex you can use both mmd and gfm syntax at the same time with one unified parser.

Yeah, that's how I felt about CommonMark, too (but I've come around). The thing I'm shooting for is not a new standard, it's a tool that implements all of the existing "standards." I'm not creating new syntax or enforcing new rules, just making a tool that means you don't have to think about which processor you're using and what extensions you might be giving up by choosing one over another.

You’d be incorrect.

It definitely is not. nvUltra is mostly out of my hands right now, my own projects (including Marked 3) are what I'm doing while waiting for the last pieces to come together.