The significant majority of markup languages essentially treat a single line breaks as a space. HTML, Markdown, et cetera. In lightweight markup languages, you normally need a blank line (i.e. two line breaks) to signify a paragraph break.

GitHub issues and discussions are an outlier in treating them as hard single line breaks (which are not paragraph breaks).

Most plain-text communication used to use line wrapping, often not supporting lines above, say, 100 characters.

Just like typeset prose uses wrapping, because your paper isn’t infinitely wide.