> There’s nothing about Markdown that says nested lists should look like code.

Yes there is. The Common Mark spec, from 2014, says 4+ spaces indents are code. Nested lists go beyond 4+ indents pretty fast.

…as long as you ignore the context that it’s a nested listed under a less-nested list.

Also, note that CommonMark is not identical to Markdown. It intends to be a standard definition of the language, but may differ from the original definition and implementation.