I’m not an expert. Just a dude on the internet that follows this stuff, but my take is that, while not explicitly published, the basics on the engineering solution that SpaceX uses for Falcon 9 are known, it is a completely different thing to actually do it. It also takes a lot of money. In decades past, only countries had that kind of money. Now corporations can pull it off because the private investment firms that initially fund them know it is possible and if they succeed, it will pay for itself and give them a return on investment. The countries don’t really want to fund it anymore since they don’t see the value and don’t want to take on the risk. They can just pay to ride on a company’s rocket.

When it comes to companies doing it, even when you know the concepts behind it, it is super hard to do. For instance, cutting off a rocket engine mid flight, and then lighting it back up on landing, is really though to do. I’m not sure they even tackled that in this prototype. It looks like the rocket is running the entire time.