3D printing actually is useful though. Basically everyone designing products or any kind of engineering is using it. The only reason it never took off for the average consumer is that every pre designed piece of plastic junk you could ever want to download and print is already available from Amazon.
In a pre online shopping world 3D printing would be far more useful for the average person. Going forward it looks like it's only really useful for people who can design their own files for actually custom stuff you can't buy.