Why the 3rd generation Chevy Cavalier only have 4 cylinders no 6 cylinders that time?

Probably because the factory decided not to build Cavaliers with a V-6 engine after 1995. They DID offer a 4 cylinder engine that made almost as much horsepower as the previous model's 6 cylinder engine, and was lighter weight, so the performance was probably about the same.

By the time the 3rd gen model came along, they could produce more power from a 4cyl then the old V6 boat anchors.

The V6 models made 130-140 hp, while the 3rd gen 2.4l 4 cly engine made 150 hp...

They were all still pretty craptacular...

Because 6 cylinder engines are way bigger than 4 cylinder engines and that's a tiny tiny baby car for tiny tiny people

The car was used to help GM meet its Corporate Average Fuel Economy (CAFE) targets so they decided to stay with 4-cyl cars. Also the 6-cyl engines had at the time would have made the front/rear balance unacceptable for driving.

After 94, they must have decided on that cruddy quad 4 style hard to service turd, apparently...Stupid water pump access for one.