I think volume and cost was never really the issue. Even if 3D printing something was 3x the cost it could justify itself just by the sheer amount of overhead it can otherwise remove. Ultimately what limits 3D printing is what you can make with it, and the fact that it doesn't remove assembly as a manufacturing step. If you could 3D print full products then I think the promised revolution would have happened. (As it stands 3D printing has already had a massive impact on manufacturing. More stuff than you would think is 3D printed now, it's just not complete consumer items)

(Not to mention, it's only in the last few years where consumer-accessible 3D printers are more than hobbyist grade that required a huge amount of tinkering to actually work properly)