> I do wonder if early world explorers had been from the southern hemisphere and a tradition of "south up" was already established, if it would still look better to us to have more land on top.

No, the preference is conventional.

I should note, though, that Chinese maps were traditionally south-up. There's no reason to expect what hemisphere people are from to control that decision.

(Not only did the Chinese come from the northern hemisphere - they had an official orthodoxy holding that the north of China, where they originated, was morally superior to the south!

Nevertheless, they drew their maps with south at the top and referred to compasses as "south-pointing needles".)

…except when they put East at the top. The compass points go 東南西北, after all.