As I believe the function of the caps/shift lock on most, if not all, manual typewriters that had it was to physically lock the shift key's mechanism down in some manner, its position above the shift key was also largely dictated by the mechanism, as it needs to be positioned along the shift key's arm.
The existence of the caps lock can be ascribed both to all-caps being more useful as a heading and for emphasis on manual typewriters, where only one typeface and size was available, as you point out, and to the substantial mechanism making it more difficult to hold the shift key down while typing.
Surprisingly, however, the size of caps lock on most modern keyboards doesn't seem to come from manual typewriters. At least on pre-1960s/70s manual typewriters, caps locks seem to be the same size as normal keys, if not smaller; shift keys are often larger, but are also not enormous. Most examples of large caps lock keys that I can find seem to start only one electric typewriters, exactly where they wouldn't seem as useful. It is possible that there are practical reasons why having a long keycap for a key requiring substantial force would be problematic for manual typewriters, but this still doesn't explain why the caps lock would become larger on electric typewriters, only why the shift might. So I'm left rather confused as to why they became the standard.
(Of course, on my keyboards, they are usually remapped to control, or to a control/escape combination.)
The existence of the caps lock can be ascribed both to all-caps being more useful as a heading and for emphasis on manual typewriters, where only one typeface and size was available, as you point out, and to the substantial mechanism making it more difficult to hold the shift key down while typing.
Surprisingly, however, the size of caps lock on most modern keyboards doesn't seem to come from manual typewriters. At least on pre-1960s/70s manual typewriters, caps locks seem to be the same size as normal keys, if not smaller; shift keys are often larger, but are also not enormous. Most examples of large caps lock keys that I can find seem to start only one electric typewriters, exactly where they wouldn't seem as useful. It is possible that there are practical reasons why having a long keycap for a key requiring substantial force would be problematic for manual typewriters, but this still doesn't explain why the caps lock would become larger on electric typewriters, only why the shift might. So I'm left rather confused as to why they became the standard.
(Of course, on my keyboards, they are usually remapped to control, or to a control/escape combination.)