They are a solution to a problem which doesn’t really exist in modern watchmaking - that of difficulty with positional variation. A well made watch can be so accurate that and benefit from a tourbillon is effectively useless. But, if we ignored all theoretical solutions to problems that don’t really exist then we would get rid of mechanical watches altogether.
However, making a good one is still very difficult and time consuming, and a good one can be beautiful to watch. Yes, mass produced and badly made ones are available, and usually in laughably inaccurate watches, but a good one is a real work of art.
They still sell for the same reason mechanical watches still sell, because they can be beautiful, difficult to make, and have a sort of romance about them...
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