Computers had no competition for their use case. There was nothing that came close to storing, processing, and transmitting information like that. The only thing stopping them from being used everywhere was size and price. If you were dealing with information, you would benefit from a computer as soon as you could afford one.
3D printing is not like that. There is already an entire set of industries built to produce widgets. 3D printing doesn't offer any benefit except for customized items. So how often do you need something customized? No matter how cheap 3D printers are, it's always going to be cheaper to get somebody else to print a one-off for you using their machine. You don't use it all day multiple times a day. You pay them for that one-off, and then you don't need a 3D printer again for a long time.