Why hasn't space tourism taken off?

Listening to Richard Branson over the past 20 years, you'd be forgiven for assuming that space was by now being frequented by lots of tourists. However, despite the Virgin Galactic chief's optimism, the space tourism industry has yet to take off. Up to now there have been only seven self-funded citizens in space. And with billionaires such as Jeff Bezos and Elon Musk in the space race, why are there still no tourists in space?

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