Let us say I want to play an Elf Barbarian. Why? Not because I want to min-max, but because I find the story potentials of an elven barbarian interesting. I can imagine some very interesting roles and thoughts from someone who has lived 200 years in the same forest, cut off from civilization.
However, that doesn't mean I want to be a bad Barbarian. In fact, being strong and dual-wielding troll-bone handaxes is part of my backstory, it sounds awesome. I can build some great stuff with this. Except, nothing in elf mechanically is what I want for a Barbarian. the lack of Strength and Con make me deal even less damage, miss more, have lower HP. Heck, if I was building this with the Standard array, I'd be looking at 15, 15, 14, 14, 10, 8 which isn't terrible, I mean, I can work with it. But my very first ASI at level 4 is going to be getting those to 16's, meaning I can't take feats which I love to take, because they are more interesting.
But, I could do a nearly identical concept with a Dwarf. Getting 17, 16, 12, 13, 10, 8. Same AC, better damage, better hp, better in every way as doing what a Barbarian does. So, now I am forced to answer a question. Do I care more about being an Elf, or more about being a Barbarian?