Again, being “bigger” is fine. The D4 Druid is not “big”, he is morbidly obese. That’s not making fun of it, that’s a serious medical problem. That’s not just “a different body-type”, that’s something that can only come from an excess of eating or drinking, or an extremely sedentary lifestyle.
People want to play characters with aspirational qualities. Blizzard found immense success in the 90’s and early 2000’s using “rule of cool” in their character designs. D4’s Druid veers way too firmly into overweight, obese territory. He does not look like the character class he is meant to be portraying, which is a character who spends most if not all of his life in the wilderness.
One could argue that such a body would be more appropriate for the Sorcerer, a class that relies on magic to solve problems. But again, we all know people wouldn’t like that, because of the reasons outlined above.
People want their characters to be cool, to be things they might aspire to be. Being large is one thing; having literal rolls of fat on their face and body is quite another.