That's really a key issue. Most "standalone" things people want are not made of plastics, except for toys. There are a some things - for example, parts for a small homemade drone or whatnot, where strength is not important but lightness is. But most often, if you want something "standalone", you want it out of metal.
Being able to print replacement plastic parts for other things could be nice, mind you. For example, I've twice had to replace a plastic part on my refrigerator and it cost something like $50 each time with a nearly month delay, due to customs fees, shipping to where I am, etc. Having been able to print one out would have been great. Except, having a 3d printer alone wouldn't have been enough, because there's no "universal spare part database" that manufacturers upload to. A 3d scanner as well might have been able to enable reproducing the part from scanning its broken pieces, except that not only do you have to have one, the part was transparent, and many 3d scanners don't like transparent objects.
A "3d printing revolution" may come some day. But things are a lot more complicated than just making it possible to print something out of some material.