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Much of it comes down to ease-of-use / accessibility. My 70 year old parents can use reddit. They could not use usenet.

You could create a usenet client with all the accessibility features that you wanted.

Reddit might be accessible, but that's because they want it to be accessible. You rely on them doing you a favour.

You could, and Dejanews / Google kind of did, but it still never gained critical mass...