Because it’s a really cool idea on many levels, and because some interesting people are willing to throw enough money at it to make it happen.
Like art & architecture, I think it’s worthwhile to do some engineering projects ONLY for the purpose of achieving an engineering marvel that will survive across generations/millennia - a kind of art.
(So long as it’s privately & voluntarily funded, of course.)
Back in the Renaissance, art was a ‘patron’ thing. It was beautiful.
Now we have government funded art that is ugly and depressing...............