For that first 60 years the movie industry had a much bigger market to sell to - in the past few decades movies have consistently lost market share to television (there used to be maybe ten channels in any given market, now there are hundreds), video games, the internet, etc. Home video has been keeping the studios alive while they continued to lose ground to all those other things.
This is why they've been so adamant about paying low residuals on home video, through numerous strikes by writers and actors etc.
And studios would love to sell their product all over the world, all the time, as much as possible. It just isn't that easy. Countries have laws about foreign imports, they have their own movie industries to protect and promote, and there are a finite number of theaters in every country. Overseas releases have all kinds of local conditions and restrictions to deal with - it's not a matter of picking a date and having theaters available. They may not be.
For example, the only countries where Carruth's movie isn't for sale online already are the very few where the movie has yet to be released in theaters. Releasing a movie in theaters requires the hiring of a distribution company who become partners in the release - they book the theaters and take a share of the profits etc. So I'm guessing his movie isn't online in those markets because that was a requirement by the releasing company. Why go to all that effort to put out a niche movie with tiny market potential as it is - if it's already online?
Movie studios are scrambling to make use of all these new markets, but it's not easy... there are an awful lot of laws and union restrictions and global trade issues to hack through. And all the while, the market for movies in general continues to shrink.
In the end, I suspect Spielberg and Lucas are right, tentpoles will become fewer, movie production in general will scale down, and that's not necessarily bad. But there will be a lot more company failures along the way, and jobs will continue to disappear and never come back.