Why does Anubis not leverage PoW from its users to do something useful (at best, distributed computing for science, at worst, a crypto-currency at least allowing the webmasters to get back some cash)

People are already complaining. Could you imagine how much fodder this'd give people who didn't like the work or the distribution of any funds that a cryptocurrency would create (which would be pennies, I think, and more work to distribute than would be worth doing).