There is one main reason, although as usual there are exceptions. Fruit seeds are contained within the skin, such as apples, Pears and Oranges. Vegetable seeds are created outside the skin. There are exceptions to this rule. Tomatoes and cucumbers botanically are fruits, but for culinary purposes are treated as vegetables. The explanation can be lengthy, this brief comment gives you an idea of the difference
A pair is a fruit, not a vegetable
An apple is a fruit, not a vegetable.
Asparagus is a vegetable, not a fruit.
tomato is not a vegetable, its a fruit because fruit has seed
It is a fruit but eaten as a vegetable
It is a fruit on the vine and a vegetable on your plate
no a colliflower is not a fruit, it is a vegetable!!! No
It is a fruit, for culinary purposes it is a vegetable
Outter skin is a fruit or vegetable
An apricot is a fruit and a avocado is a vegetable or an aubergine
Mustard is not a fruit or vegetable, it is a condiment.
its a tuberous root, which can be considered as a vegetable. its not a fruit for sure!!