Fender design question

[ChevyRacefan]

Hello,
I am not sure if this is the same for all years, but my '71 the lower part of the fender in front of the wheel, on the inner side, has an area that is just the right size to store a qt of oil, transmission fliud, etc.
When these were new, oil cans were round.
Was there a reason, use for these little pockets other collecting crud, back then, before qt. containers that now look like they were made to be stored there.