you are forgetting the composed video output. A scart adapter like the one used for old PS and you are done with 99% of TV around the world.
You are forgetting that most school computer labs will be equipped with PC monitors with VGA inputs.
Not many of those have composite inputs.
Did SCART ever catch on outside of Europe?
The BBC micro had an 80 character video mode; that was virtually unusable on a composite input too, unless you had a really good chroma filter - you really needed a dedicated mono monitor to use that mode.