3D printing isn't the future of mass manufacturing, but it is getting much much closer to being the future of prototyping and one-offs for pretty much every plastic thing (and some metal ones, too), especially as the hobby level printers keep getting better.
If you're not impressed with this, you likely haven't ever gotten quotes from a quick turn plastics manufacturing shop.
Who on earth would want to make a computer case from plastic? Cutting, folding, drilling and riveting sheet metal is fast and economical, even with basic hand tools. You can buy a dizzying array of fixtures and fittings from McMaster-Carr or your local equivalent.
I'm not fundamentally opposed to 3D printing, but I do have a bone to pick with the "maker community", which seems to have a pathological aversion to basic shop class skills. If you want to make a custom PC case, then by all means do so, just don't stink out your house with ABS fumes in the process - buy a copy of Basic Benchwork by Les Oldridge and Sheet Metal Work by R.E. Wakeford, scrounge up some tools and have at it.
In many, many cases, most things done by "makers" can be done without 3D printing anything, and be more accessible to others. I can understand needing or using one when you need something custom to fit or retrofit into an existing commercial product. Even there, with a bit of thinking, one can generally come up with a solution where a 3D printer isn't needed.
I'm starting to see this same kind of attitude creep into laser cutters - projects that seem to think everyone has access to one, when that isn't necessarily true. For instance, I know where I could go to get access to one (and 3D printers, etc) - but it would be about a 50 mile drive for me. Far enough where I would seriously consider other alternatives.
I do have to say, though, that the 3D printer (and other CNC tools commonly used by the maker community) has allowed for a lot of people who may not have the dexterity or other related abilities the chance to design and build some fantastic creations. Furthermore, there are more than a few things that just couldn't be done any other way (or at least as cheaply or quickly). There is also the nice idea that (at least in theory) one can take those same files and use them with other CNC processes. In the case of laser cutters, if you can print the files full-sized, you can even cut them out manually with a coping saw or other more "manual" tooling.
FDM printers, from what I recall, existed as commercial products for prototyping long before reprap and other early hobbyist efforts came to fruition:
https://en.wikipedia.org/wiki/3D_printing#History
...and according to that link, even more advanced processes (stereolithography, for instance) were being explored in the 1980s and 90s.
These systems have long been available on the commercial market - albeit for (likely) a steep price. What has really happened is that the price on the systems have dropped steeply, and they are now available to the hobbyists with the skills to use them.
Before, that was a near impossibility unless you worked for a company that had a commercial system - and would let you near it.
What has really happened is that the core patents on FDM technology expired in 2009, resulting in an explosion of new approaches to the technology and now you can buy a home unit for well under $200.
3D printing isn't that terribly complicated and the required hardware has been around for decades. The only thing that made it expensive was rent seeking.
Just look at all of the custom parts that went into this.
https://blog.briancmoses.com/Images/2019/mymk735/brians_mk73...
3D printed drive rails and hinges is honestly a pretty bad idea even for a prototype, and it basically doubled the time it took him to assemble it. I'd say it's a pretty big leap forward that some average Joe can print out a custom case like this and have it come out looking fairly professional.
But of cause, this article does in many ways highlight the problems with current 3D-printing technology, and why it currently is mostly a rather limited prototyping tool. This would be the case even for more professional 3D-printers. Now most of the hype is gone, and I think most people realize that 3D-printers will remain a prototyping tools for the forseable future.
It's an advancement and we are the early adapters.
Even in the current state, I managed to print many useful things, only by downloading 3d models by the fraction of the price I would be paying if I were to buy those things from shops.
I also realised that 3d printers are not the same as few years ago, they are more precise, accurate and handling the errors better than previous models.
So I am a bit more hopeful than you for the foreseeable future. :)