Here are some of the reasons:
* Different Orders: Sharks belong to the order *Selachimorpha*, while dolphins belong to the order *Cetacea*. This signifies a very distant relationship between the two.
* Different Reproductive Systems: Sharks lay eggs or give birth to live young, while dolphins are mammals that give birth to live young.
* Different Anatomy: Sharks have cartilaginous skeletons and gill slits for breathing, while dolphins have bone skeletons and lungs. Their body shapes, fin structures, and internal organs are also vastly different.
In short, sharks and dolphins are too different to produce offspring together.