[Symbiote]

That claim needs some evidence. Is there a good example? All the sites I can find are either toys or archives of university sites from the 1990s.

From those sites:

There is a lot of completely inaccessible ASCII art.

Everything is shown in a plain monospaced font, including tabular data. Emphasis can only be done using asterisks, capital letters or similar.

Images can't be embedded with context, only linked to -- at the end of the document.

Links can't be shown in context, only at the end of a document.

Only ASCII text works.