Like most appliances, there are different ones made for different reasons.
Most ovens are made "standard", which means they basically heat up to cook something.
Some ovens are a bit more specialized, as they may have "extras"....which can be anything from having a light inside the oven, to being convection (which means there is a fan inside the oven circulating the air).
There are also differences in the way they cook or bake. There are electric ones, gas ones, light sourced ones, and microwave ones.
Some ovens are made for baking, some are made more for broiling or roasting, and some are made for slow cooking.
Depending on what your main intentions are for needing an oven, will be the basis for what kind of oven you should have.
Now dishwashers on the other hand.....................
Never understood why there has to be 200 different kinds, when all it really does is just wash dishes. You stick your dishes in there, press a button or turn a dial, and it washes the dishes.
No reason to have more than one kind.