Because few people actually care that much about their privacy. Compare the existence of social networks, which exist for the purpose of people being less private.

The vast majority of people want to purchase things as simply and cheaply as possible. And that's going to mean not paying a premium to purchase their money from other people. And since they'd be buying it via their existing non-anonymous means, it wouldn't do anything anyway.

If an economic system already existed, so that people could receive their paychecks in a cryptocurrency and spend it freely at any store, they'd accept that. But anonymity isn't going to be all that much of a draw for anybody who is used to making purchases already via non-anonymous means. The only people who feel compelled to do so are those purchasing things illegally -- which just makes people who would want to purchase things legally even less interested.

tl;dr: Privacy advocates put a lot more weight on anonymity than most people do.