The Commodore PET had an all-in-one form factor where the monitor was fused into the rest of the computer, making a single unit, not dissimilar to some early terminals like the VT100. This is undesirable; it makes the computer hard to lift safely, the monitor impossible to position ergonomically, and if either the main unit or the monitor goes on the blink, you can't swap out or return just that part; hence, later computers moved away from this design.
Given the undesirability of this design, why was it done? Is it substantially easier or cheaper to design that way?
Does the answer change when you move from early 10-12" monitors up to a full 14" monitor?