Corsets work becasue of the boning, usually steel boning, that pushes down on the waist.
And by pushing down on the waist, the tissue -usually fat, sometimes muscle- is pushed either up or down which makes the waist look like & become more cinched in.
Certain corsets may also push in the floating ribs which can cause the waist to look even more reduced.
Think of your phone and how you hold it.
Stay with me.
I hold my phone with my pinky on the bottom of it.
Overtime, the weight of the phone has created a tiny little dent on my pinky.
Another example is of when gamers who wore head sets all the time noticed they were getting a slight inent on their head.
None of this is “natural” per se, but also none of it dangerous.