I'm glad there are multiple players in this space so they can compete and drive the cost down over time.
Answer: exclusivity.
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Or to explain the topic in economic terms: with their offering, these companies offer a given supply for balloon rides into the stratosphere. On the other hand, for a given price for such a ride, a demand to buy it for this price. What a company wants to optimize is
(number of sales for a given price) * price.
Since the supply is currently rather limited, the price can be set to a very high value to optimize this function.
They need to make back the cost of R&D. IE, based on how much it costs to design and certify the balloon, the first flight might operate at a loss. They will need to perform X successful flights before they break even on the cost of R&D.
IE, it might cost $10,000 to pay the staff on the balloon ride, but the vessel itself might cost 10 million to design. It might use $200,000 worth of parts, but the factory cost $20 million to build. Those costs need to be amortized by paying passengers.
I'm sure the cost will come down, just like everything else. See https://en.wikipedia.org/wiki/Economies_of_scale
Simultaneously, from all sides sellers are now constantly testing the elasticity of consumer budgets to maximize profit until they exclude the bottom x%, it's a huge financial strain for the poorest among us.
That’s kind of the whole point of the capitalist / consumerist model: first movers take high risks with investment and can reap outsized returns if successful, while success breeds competition from new entrants who have a proven market and a product to copy. The expansion of the market means more price competition, driving prices and returns down.
I’m not saying it always works like that, just that it generally does.