> Not only that but Markdown use the conventions people already used in text files

So why not Markup? At the time, everyone was using markup because Wikipedia was in wikimarkUP, with # for numbered lists, {} for macros and === to denominate titles. The latter still works in Markdown, but the former doesn’t. Funny heritage: Confluence shortcuts are also expressed in markup because it was the trend at the time, but they changed the shortcuts when they went to the Cloud.