there is nothing "basic" about this. something that seems pretty obvious to you may not be natural to someone else.

i think the single-click navigation or opening of files was done to mimic how hyperlinks on the internet work. some people are wired that way.

on the other hand, some people have a completely different brain configuration: they think that a single-click should select whereas a double-click should open a file.

there are people who do not agree with both these options. maybe, they want everything to work via audio commands.

how do we decide what the default behavior should be? the answer is: leave it to the user.