However, in this particular trajectory, SpaceX did build the rockets and did build Starlink which is now the best global-scale wireless communication network for many use-cases. Stretching this trajectory to scale up the technology to facilitate in-space computing is vastly more grounded than Shakespearean monkeys.
That's the case on a pure "I could invest my money in something that makes a bigger profit now, and use that money to buy shares in the longer term bet afterwards" basis, but is even more the case when you factor in uncertainty. And "SpaceX's 2026 near monopoly of launch and the 2026 datacentre build rush will still be relevant once we're far enough into the future for inference chips to not need regular replacement and orbital megastructures to be cost competitive with ground ones due to the amount of orbital recycling going on" is pretty uncertain...
The large variance is in the projected market size, but I can see why people might be optimistic. Especially given SpaceX's success in Falcon 9 launches, gradually stealing stats away from the record-holders, who have been mostly Russia/USSR-based[0].
[0] https://spacestatsonline.com/rockets/most-launched-rockets
That sort of long run probably has even longer timelines than 75 years, and that's an argument which carries almost zero weight to an investor (particularly relative to the one SpaceX is actually making which is using their launch monopoly to make massive profits meeting 2020s inference compute demand) because by the time it happens, assuming it does, the space market is unrecognisable and they've missed a whole bunch of other hype cycles. The bull case for SpaceX depends a lot on what they deliver by the mid-late 2030s being more than expected rather than less and essentially not at all on the constraints and challenges of next century.
[1]I also hear this thesis every week from my own CTO, but much as some VCs like the passion it's not why people fund us...
On a serious note, if you think that everyone else loses contact with reality, it's a signal to check and recheck your assumptions.
If it were only retail investors, your assumptions could make sense.
However plenty of the share ownership is institutional investors. Most of them care a bit more about fundamentals. (I'm ignoring passive investors just using indexes).