Couple of random thoughts:|
1). Relatively recent innovation? From looking at the dates of these things, a lot of the symbols are relatively recent. Some of the older symbols are a product of the 13th thru 17th century, but much of the set symbols are in the late 19th century.
2). What happened to all the dead ends? For every notational device that eventually got accepted as standard, I'd speculate there were hundreds that failed to catch on. For those that used non-standard notation, it probably means that over time only a handful of people will be able to decipher the meaning of the text. And more confusing is probably those that were closest to the standards, but have just enuf differences to make them confusing. (For that matter, notational standards aren't a fixed point - they are evolving with twists and turns along the way).
Finally, I think mathematical notation is both a boon and a curse. A boon because it allows one to express ideas in an economical and precise manner. A curse because it presents a barrier to a larger audience - even though many of the ideas behind the formulae are simple and can be understood without resort to notation, the very presence of notation will have the effect of restricting the audience (of course, this is not always a bad idea).