The reason some peoples poop smells worse than other peoples poop is usually due to the extra fat that some peoples poop contains.
Poop that contains a lot of fat can smell worse than other peoples poop that contains less fat.
The really bad smelling poop can be caused by your diet being different than others and if you eat more fatty foods such as meat, hamburger, steaks, pork etc then your poop might smell worse than other peoples poop.
Poop smells bad regardless of who you are because the poop is made of undigested food, bacteria, mucus and dead cells.
But some peoples poop may contain more bacteria or mucus or more fat that can lead to the poop smelling worse.