Lower-case was not common on printers and terminals in the 1950s and 1960s (and into the 1970s).
The Apple II computers, for example, had only upper-case characters in ROM (and screens were 40 characters wide). Lower -case characters would have required a second ROM, which obviously increased costs. Eventually models with lower-case capabilities were added, as was 80-column output.
No, in some cases there were not. In addition, capitals served as a method of differentiation for language keywords and such.
Maybe worth to add that syntax highlighting was not a thing back then.
Not nearly enough cycles for that. Nor core memory. Nor even the possibility of colours or font styles. You were lucky if you got a timeslot for your program and didn't get preempted. You were even luckier if you got both uppercase and lowercase letters. (-:
* Nearly all this was before my time.
Ancient languages ran on ancient machines with 6-bit character sets. No available way to key in or print lowercase letters.