Small form factor computers are almost as old as mainstream personal computing. I remember things the keyboard units like the Commodore VIC 20 and 64. I had an Amiga 500 at one time, and there were other similar Amiga units like the 600 and 1200. The Amiga 600 was tiny!
One small footprint computer I only ever got to see in person and use once belonged to a friend of my fathers in the late 1990s. This was one of those IBM Aptiva S computers that used a long cable to connect the media unit (CD-ROM drive, 3.5" floppy, speaker, keyboard, mouse, monitor connections) to the main CPU parked in a convenient location some distance away, to free up desk space. I don't think they sold very well. I remember them being marketed, but that was the only one I ever saw.
The thing about Apple is that they bring their industrial design expertise to the problem, which is why their products are more elegant than most others. For example, if they were inclined, they could probably build an attractive keyboard computer based on the Mac Mini internals, and spread the connections across the back of the unit and put the Amiga 1200 to shame and it was a pretty decent looking computer - which is remarkable considering the time it was made and the fact that it was designed by Commodore.