re: only 3.5% of traffic using z-addrs:

The dirty secret of crypto is that there is almost no economy that exists for any of the altcoins, and relatively little even for Bitcoin (which functions as the reserve currency due to its lions' share of the economy).

Effectively, by volume most altcoins are held by either miners (who sell immediately), or daytraders who will pump and dump. A very small fraction is held by true believers (who will HODL under all circumstances), but they don't contribute to the economy either.

Such people don't care about anonymity, they're not actually using the currency, they're just traders, and traders mostly don't need to be anonymous.