For the same reason people have home 2d printers, they will have 3d printers.
The reason people have home 2D printers is because they generate a huge amount of 2D data, some of which sometimes needs to be copied onto paper. Most data we put to paper is generated very soon before we print it, and the time we have to wait for it matters because once it is printed we usually spend very little time consuming it before disposing of it or filing it away.
We do not generate large amounts of 3D data, especially not the kind that we need to create in a physical form, and especially not the kind that is needed at short notice.
The applications you list (prototyping, repair, modelmaking and molding) are things that 90% of people would never do at home, and those that would will find in perpetuity that (unless they have a hobby that involves high-volume manufacture of one-off objects) on the rare occasions when they do want something made, the nearest commercial 3D printing service will be a more satisfactory solution than the more expensive, poorer quality, and most likely slower, 3D printer they could have cluttering up their home.