I think that’s what happens when you wear pants too big for you - the extra material has to go somewhere.

I know it’s not intuitive, but taking in the waist - actually reducing the waist instead of just cinching it with a belt - can help with crotch bulge. You take it in in the back, so that the front is pulled tighter and lays flatter; some excess material is removed, and the rest ends up in the back where it’s not as noticeable.

www.wikihow.com/Make-Your-Jeans-Tighter

I’d suggest practicing on a pair of jeans you don’t really mind putting holes in first - I totally screwed up the first time I tried 😆