[AgentME]

It relied on a central authority to work, and that's very related to why it no longer works.

[wruza]

David Chaum opined then “As the Web grew, the average level of sophistication of users dropped. It was hard to explain the importance of privacy to them” https://en.m.wikipedia.org/wiki/Ecash

Not sure how this opinion relates to failure, but just in case, things only got worse since.