Courier was the default typeface of IBM typewriters for decades, monospaced mechanically just like everyone else.
No difficulty producing columnal or tabular data on the first attempt was forseen.
When FORTRAN programming came along, you wanted the characters to line up in columns properly too, expected with the simple dot-matrix fonts.
Daisywheel printers all had mono Courier, with some starting to also autodetect mechanical PS printwheels when inserted.
Dot-matrix printers got better fonts than DOS itself but what you see on the screen was not very much of what you got on the printout the first time. PS could increase woe. Courier was available both ways. But tons of people stuck with the simple characters like you get on the cheap store receipts.
DOS text files using a monospaced font can be reselected to a different monospaced font without all the formatting difficulty you can get otherwise.
When Windows got popular, loads of people found out their old dot-matrix printer had been capable of beautiful PS output the whole time, it had just been out of reach without a WYSIWYG drafting approach.
You can still set your email window for a monospaced font, and draft a message into a Notepad window set for mono, intentionally with all the sentences of each paragraph on a single line when Word Wrap is disabled (disable Word Wrap before copying & pasting), and with a single line space between these _paragraphs_.
Then just copy & paste the whole text linewise from Notepad to different email windows and their mono spacing can be a good way to make the different local & remote word wraps work with less headaches.
Courier's remaining universalness still makes it a top choice for this type of thing, but a new monospace font that can serve as a functional superset is good to have.