Because they look like eggs. Hence, eggplant. :) For 30 years or so, I only knew of purple eggplants, and only one or two varieties of purple at that. Having taken but never learned much of the French language, I always thought “aubergine” was a really nice name for them, and the color aubergine or purple of sorts, made sense. But about 15 years ago, I saw my first “real” eggplant, a variety that quite literally looked like a large ivory white egg.
I have written about eggplants before, with several varieties photographed in a previous post, here. And the photo above adds several more types of eggplants to the album… Fascinating stuff, eggplants. :)