You have to think in the context of what a GUI represents at the time. Your assumption was based on the command line ethos, where Enter key plays an important r

You have to think in the context of what a GUI represents at the time. Your assumption was based on the command line ethos, where Enter key plays an important role. It was true on Apple II command line too, but the original Mac interface was designed to do away this keyboard centric mindset. "Use your mouse" was the philosophy behind it. The original Mac keyboard didn't even have arrow keys, it encouraged a novel way of interacting with a machine that is so different to anything before it. Also, the Enter key that represent so much importance to you, on an Apple machines it's always "Return", which is nothing more than a carriage return, strongly linked to text inputs. A Return key does not "enter" anything. Return and Enter are two completely different keys to the OS. Based on the design choice, Return key deals with text entry, rename is probably the only reasonable text entry function to a file explorer at the time (or even today). This Return vs Enter design choice has been consistently applied on all Apple machine ever since Apple II, which predates any windowed OS you care to mention.