Why has markdown become so popular?

Markdown is a compromise between plain text and a complex rich text. It’s readable as plain text AND can be cleanly rendered nicer if the location supports it. It’s storable as a string without having to consider anything special about it. It can be written in plain text or a rich text editor so it’s flexible. The most interesting trend though is towards Medium, Notion and Coda where formatting is constrained and results in more consistent and cleaner documents. Markdown is constrained in what you can do similarly and benefits from this trend in consumer tools.