Very few useful tools or machines are 3d-printable, due to tolerance and strength constraints.

Not trying to be rude here, but have you designed a plastic part for production? This isn't remotely practical for many if not most applications that I have seen. Cost, tolerance, surface finish, yield are all major issues. It's also far less automatable than injection molding. Post processing an SLA part for example is very manual, injection molded parts come out of the tool ready for use. What do you think is going to change about that?

It is not a universal solution, both because it's slow, and because of various limitations and faults it introduces. There are dozens of manufacturing processes, some of them fairly new and modern, that will never go away.