I don't entirely agree with what they have to say, especially when they search for a possible target chemical, but they provide a whole bunch of contradictory evidence against the naive laziness hypothesis. Of which the most convincing argument is lab animals: https://royalsocietypublishing.org/doi/abs/10.1098/rspb.2010...
Lab animals do not have control over their diet and activity level, and yet are becoming more obese.
1. They haven't found any mechanistic evidence to support this.
2. All of these populations had access to manufactured food. (Either human or pet food)
3. This is really only one study, not really a field of research.
IT seems like the theory manufactured food has gotten tasty since the 80's would also explain this data.