I should have added an example to my question, so here, belatedly, it is:
Why should any company invest in advancing 3D printer technology by committing time and money to research and development of better printers if they can simply take it for free in a few years?
I know, it is counterintuitive...
But your same argument would apply to the internet. Why invest in internet infrastructure if it will end up making information that everyone has to pay dearly for now... not have to do that?
Why invest in advancing metal production if everyone can buy a 100 pack of razors for $10 when each hand crafted razor is worth $100 now?
There is money to be made, just not on the end it has been made on. Complete complex products will still be needed and that demand will never go away in our lifetimes. But simple items? Maybe there will be no market at all for single-material products in 30-50 years. You’ll just punch up a free design number from the internet for any one of a trillion items...
This is a mental exercise about as difficult as sitting around 25 years ago and trying to accurately imagine what we would be using the internet for today. The changes will be that vast. Back then, if you couldn’t get it in a library... ? Or instant ordering of almost anything on earth through Amazon? The internet has been a net gain for the world, even if it has caused horrible disruption and growing pains in certain areas. 3D printing will be the same way.