What WAS their motivation??? Excellent question! Let's go back to basic psychology class & Freud's levels of the mind. The OP said that they noticed people asking overweight people im particularly, more about food. So this is not a single instance.

How many things do we do consciously, with full intent......& unconsciously almost like a passenger, but when the issue is brought to the conscious surface it's wiped away. Excused. Not related. Like calling this person an a hole or different types of shaming don't exist. In your consciousness they might not.

And yes there is kink shaming. Ask my large munch group that has black balled me, asked me to leave & not return. Yes there are many a holes, but that's a blanket statement & fixes nothing.