Not to detract one iota from this amazing achievement, but what definition of sustainable are you thinking of? This was still paid for by the government.
The government paid for Apollo. And once they decided they no longer wanted it, it became impossible to use Apollo parts, technology, or any of the engineers or technicians to put people into orbit. The capability "vanished."
If the government never bought another ticket to space, Crew Dragon could be made available to people who want to go into space and are willing to pay for a ticket. So even if NASA got defunded completely tomorrow, the ability to go into space would still be there. Because the market for space, when served in an economic way, is self sustaining.
This has never been true before, and now it is. That is my definition of sustainable.
There are 4 unnamed tourists set to fly next year. Tom Cruise is also in negotiations to film in space using Crewed Dragon, which would presumably involve at minimum Mr. Cruise plus a cameraman.
SpaceX owns the Crew Dragon IP and tooling, and they can sell flights to private citizens - in fact I believe they said today that they are contracted with Space Ventures to fly 4 people next year. Previously Space Ventures could only buy from the Russians.
All of this combined means that SpaceX is still highly dependent from the goodwill of the US government.
You need manufacturing base and a business model to sustain commercial operation. NASA is a government agency that gets its priority sets by a congress that is not very interested in space flight, and putting the budget wherever they want at any given time. So NASA could have lots of IP about 4 different vehicles that gets into LEO but no amount of money could actually get you there.
They can give the IP to a 3rd company of course, but because they way it was designed it would not really have any commercial use, and likely it only works connected together with other government IP/hardware that you also easily get.
Now you have a private company, who has a very clear business intensive, to get the greatest possible use out of that IP, it only uses other commercially available tools and has synergy with other parts of their business that also has other commercial uses. The industrial base and teams are sustained, and not removed when congress lowers budget for a year.
So the Dragon 2 works with Falcon 9 rocket. SpaceX always operates Falcon 9 launch pads and they have plenty of rockets to fly and a manufacturing base that makes more of them. So now you have a much easier time to get the whole system together for an actual 3rd party flight, as the rocket, launch pad, infrastructure is already there and commercially operated.
NASA had a great deal of knowledge from previous projects which they shared liberally with SpaceX from very early on in their development. Engines such as the Merlin are heavily influenced from NASA IP.
So in essence NASA still is a clearing house of knowledge, and much of the info learned by NASA and SpaceX to date continues to be shared with other providers to the benefit of all.
I do agree however with the sentiment that SpaceX can sell seats or rocket flights in a way that NASA was never set up to do.
Isn't the output of the US government in the public domain? I think the issue was more about the manufacturing and launching of rockets being highly regulated for obvious reasons.
[0]: https://en.wikipedia.org/wiki/Space_Shuttle_program#Budget
[1]: This article states the per-astronaut cost paid by NASA on a Crew Dragon mission is $55M, compared to $86M on Soyuz: https://www.cnbc.com/2020/05/26/spacex-demo-2-nasa-astronaut...
NASA gave a $55million estimate on cost per seat on crew dragon, which would be about $440 million to launch 8 people.
Not sure that is factoring in reusability once they are willing to use that for crew missions (or offset price reusing crew boosters on non crewed missions).
Another issue with shuttle was reliability though. It may take hundreds of flights to know how much it is improved with crew dragon, but it seems to have better launch abort capabilities etc.
Stuff like spacelab missions can probably be done using the ISS. Some of the military capabilities are moved to X-37.
Certain of the satellite launching capabilities of the shuttle were hampered by safety concerns post challenger/columbia.
The ability to retrieve and return large cargo is still missing, but it doesn't appear many people are clamoring for it. It'd be nice if we could continue to service Hubble going forward, but that's mostly nostalgia talking.
The Shuttle was supposed to do everything for everyone and it met with predictable results. The promised economies and launch rates were never realized. The safety issues inherent with the design made its continuation nearly impossible.
Having cheaper, mostly reusable launchers that have capabilities that people actually use is way more valuable.
They'll have to stop blowing them up, but at two prototypes per month I think they'll make rapid progress.
The shuttle didn't have any real abort capabilities (other than very late in the flight, when they were already in space, just not in the correct orbit). It had some crazy schemes for earlier stages of flight, but they were never tested, and no one actually thought they would work.