More likely because the whole point of Markdown was to be embedded in text, not a freestanding format for an entire document.

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leejoramo a day ago | parent [-]

This is exactly why.

It is my assumption that Gruber chose ‘.text’ over ‘.txt’ for several reasons. To give it a little difference when searching for files. To be more legible to non-computer people. And finally, while Classic MacOS did not use file extensions, the Resource Fork type code for text files was ‘TEXT’

	▲	SllX a day ago \| parent [-]
		Also a little extra distinction: “.txt” is a relic of 8.3 DOS filename conventions. He was not bound by these. If you’ve got the space, of course you’ll go with “.text” over “.txt” because text is the input, HTML is the output, Markdown is the tool for converting one into the other, per the first line of the introduction: > Markdown is a text-to-HTML conversion tool for web writers. Ergo they’re not Markdown documents, they’re text files that can be converted into HTML using Markdown. https://daringfireball.net/projects/markdown/