Verbosity was a huge argument against <picture>. People were ridiculing it with complex use cases that required awful amounts of markup.

Hixie was against using elements, as it's harder to spec (attribute change is atomic). Eventually <picture> got a simplified algorithm that avoids tricky cases of elements, but at that point srcset was a done deal.

At least we've got separate media, sizes and srcset instead of one massive "micro"syntax.