It dates to the time when typewriters were new-fangled inventions in the latter end of the 19th century. In those days, it was still common practice for typeset

It dates to the time when typewriters were new-fangled inventions in the latter end of the 19th century. In those days, it was still common practice for typesetters to use a larger space between sentences. Typewriter users mimicked that practice. Typesetting changed in the 20th century, now it is more usual to use a normal word space. Perception or ease of use has little to do with it.