Dwarves are built more like heavyweight boxers. Designed for strength over speed. They're short with compact thick muscles. They have a con bonus. Where are you seeing tubby?
Elves/Eladrin are built with long thin muscles which is true to a race that has a dex bonus. They're built like runners.
Both races are commonly depicted in shape just in different ways.
It's not about "bare mid-drifted babes or badass athletes." It's about pictures that actually match the stats.
If you take the stats of the average D&D character, but then depict it with a dumpy overweight old man, you're not really doing an accurate representation. The two adventurers depicted are a bard and a warlock. Chances are both of them are going to have pretty decent stats, and pretty decent cons to boot.
You can depict the average gnome any way you want, but an adventurer probably isn't going to match it. Just like your average adventuring human isn't going to look like the average human. He's got to be in shape, otherwise he's not going to last that long.
The average D&D adventurer spends his time unable to overeat, walking long distances, fighting with weapons, dodging monsters, dodging weapons, and otherwise just being active. He's going to be in shape.
If this were a picture of some commoner gnomes in gnome village I might agree with you. But they're not, they're adventurers.