I'm assuming it started in the late seventies, when corporations started wanting to get involved in the space business on their terms. There's tons of failed dreams starting in the eighties and continuing until today that were trying to do what happened today -- a private-industry spacecraft.
For example, my dad dug up the second issue of Smithsonian Air & Space magazine from the eighties and it had advertisements for space tourism.
I remember my first look at SpaceX. They dragged the mockup Falcon I rocket, which fits into a perfectly highway-able trailer form, to DC to show off what they had in mind. And I wasn't impressed. They weren't sexy or revolutionary or anything like that. It was just another phallic rocket that comes apart mid-flight that would launch fairly lightweight cargo.
On the other hand, unlike all of the sexy designs that were floating around, SpaceX kept moving forward while everybody else went bankrupt. And they rapidly stage-managed a bigger booster. First it was the Falcon V, then eventually the Falcon 9. And now, we're at the point where SpaceX is the rational best direction forward for America in space.
If you look at the NASA technical reports archives, you'll realize that there's a wide variety of potential technologies that were invented during the heyday of the space race. Aerospike nozzles, airbreathing rocket engines, exotic propellants, and so on. But SpaceX doesn't use them. Nothing at SpaceX is actually revolutionary. There was very little experimental or especially advanced technology they developed. It's just that they developed their own set of hardware with an eye towards making it less exotic and more practical and ignored the standard aerospace contractors if they were too expensive.
If you look at a lot of the companies and even revolutionary NASA projects, you see that they assumed a set of advanced technology developments that didn't quite pan out nearly as well as they would have liked and then found themselves with an under-performing craft that wouldn't make orbit.
If you look at most of the other companies, they happened before some quiet de-regulation manuvering where NASA lost the ability to deny companies the right to fly.
And, there were a few attempts that had what was arguably a valid plan but merely ran out of money. I largely blame this on the earlier failed startup companies. Any investor looking at funding a startup who does their research is going to see how many brilliant attempts failed. Even NASA doesn't get it right. But Elon Musk has a giant enough pool of cash from his previous venture. This makes a huge difference.
I've been writing about an inflection point in space exploration. I think we're about to reach the other side of it, where space exploration gets really interesting again.
This is rapidly justifying Obama's cancellation of the Constellation program. In 2004, when Bush's space program to nowhere was being constructed, you could easily discount the notion of NASA buying services from the commercial market as a pipe dream. By 2009, both NASA and SpaceX were behind schedule, but NASA was really really behind schedule to do even a basic replacement for the Soyuz. But given that SpaceX has two flights in a row with a spacecraft that does just about everything that the Orion capsule was supposed to do, except that it's lighter and costs far less, we're rapidly reaching the point where we can use the 2000-2020 time period as an example of the sunk costs fallacy.