> I keep seeing people wanting to build distributed this and distributed that. According to Wikipedia, usenet was already distributed. Why did it die?

People like distributed things ideologically but practically speaking they have a ton of drawbacks. It failed because it was outcompeted by centralized solutions that could leverage their centralized power to make a better product (e.g. handle spam among other things). The decentralized aspect also means incentives can become misaligned where people who are paying for it aren't really benefiting or controlling it (i imaging alt.bibaries was not cheap to syndicate)

> follow-up question, what about freenet? Are they the same thing?

No, and generally pretty unrelated.