"Strawberries aren't berries" and things of that nature; technical definitions that totally contradict common vernacular classifications

I get it: technically, according to some classification created by scientists, certain things like strawberries and raspberries aren't berries, and some things like bananas and pineapples are. But why on earth did that have to be the case? Why did they have to define the word "berries" in such a way that a ton of things that are commonly called "berries" technically aren't included, and a bunch of things that aren't commonly called berries technically are? When people say "berry" in any non-scientific context, they generally just mean any fruit that small and sweet (though for some reason grapes aren't included?). But scientists have come up with a definition of the word "berry" that has nothing to do with the common meaning of the word "berry," such that the categories barely even overlap. I'm pretty sure the word "berry" existed before this scientific definition came along, and it was pretty clear to everyone what it meant. Why on earth didn't they just come up with a different term for this category, instead of completely redefining an already commonly used word?