The reason is simple: cost + risk. It's easier to come up with the much smaller amount required to fund Instagram than to come up with enough to fund the Hyperloop. Less money is at risk. It's that simple. There may be other factors at play, but this is by far the most important.
This. And related to risk: When a website fails, it doesn't hurt anyone; if this tube were built, and then found to have a fatal design flaw, the liability would be enormous.
