Every woman doesn't put on weight the same. If some women just pig out on mcdonalds then all of that fat is going to their stomach, their arms, and their face is going to look fatter and disgusting.
Then we have, PAWGS for example

For some women when they put on more weight and work out their thighs and ass get thicker. They can still keep an hourglass shape while having curves in the process. Women that don't have good genetics like that will have to spend money to have work done if they want to look like the PAWGS posted in the OP.