I like the lawn gnome style better.
As a side note, if you pay attention to the text it's pretty clear that gnomes become lawn gnome like as they age.
I really don't think attractiveness is the issue here:
Goliaths - who btw seem to be default a bit thick - are covered in warts.
Tieflings got devil looks, horns, and tales. The high cheeck bones and svelteness work for them but not the otherwise overwhelming sense of wrongness.
Halflings have square ears, and, though fit looking, don't necessarilly got a lot going for them otherwise.
Shiters got the light fur and reverse tear drop extreme faces.
Half-Orcs got all kinds of issues.
Dragonborn - I get the scaly thing, but I don't know that that's a useful general argument and their heads and faces aren't built for attractiveness so much as robust alieness.
I could accept the Only Marathon runners need apply theory, but that runs in violation of the non-Martathon runner physiques who adventured in the past.
It could be that fatness is just a special case of a particulalry objectionable trait worse than all others, but that also seems unlikely.
So I'm guessing it's probably a combination of new conventional tropes in fantasy art abandoning the 'chubby fae trickster' trope and issues of 'adventuring physique' possibly mixed with some idea about social responsibility.
It's important to recognize that this isn't just to be laid at WotC's fault. They solicit art from a community that has its own cliches, tropes, and larger patterns.