Thick, IMO, and my opinion only, is just another way of saying slightly fat.
I personally hate "curvy" "thick"... Curvy means a woman has curves to me... And, when I think of curvy. I think of a thinner, hour glass curvy, not an overweight curvy.
Thick... just sounds.... stupid and awful. How can you describe a person as thick? Well... it used to mean dense... stupid... sounds really positive, right?