For the same reason cucumbers and tomatoes are considered vegetables when they are in fact fruits. Merely the manner in which they are consumed: Fruits tend to be consumed individually as a snack but vegetables tend to be consumed within a meal. I know some people eat both fruits and vegetables in meals and as snacks but on the whole that isn't the norm. Besides, by definition, a vegetable is a plant that is consumed. So going by definition all fruits are vegetables anyway, merely a sub-class.

This question has raged on AB and elsewhere for generations. Short answer - peppers are botanically a fruit but culinarily a vegetable. Fruit has many definitions, only one of which is 'the sweet edible reproductive body of a seed plant that is commonly eaten as a dessert.'

1) "Some vegetables which are botanically fruits (such as tomatoes) are considered to be vegetables in the culinary sense." Source: http://simple.wikipedia.org/wiki/List_of_vegetables 2) "This is a list of vegetables in the culinary sense, which means it includes some botanical fruits like pumpkins and doesn't include herbs, spices, cereals and most culinary fruits and culinary nuts. Some culinary vegetables (seaweeds like nori) are not even members of the plant kingdom." Source: http://en.wikipedia.org/wiki/List_of_culinary_vegetables 3) "I find it interesting how what we call fruits and vegetables are often misnamed. Everyone knows that tomatoes (http://en.wikipedia.org/wiki/Tomato) are a fruit - in fact a berry. But strawberries (http://en.wikipedia.org/wiki/Strawberry) are not berries, or even fruit - they are actually a vegetable, and their seeds are the fruit. Raspberries (http://en.wikipedia.org/wiki/Raspberry) aren't berries either - it is an aggregate fruit. Each little bit is called a drupelet. Peaches, plums, mangoes and olives are also drupes (http://en.wikipedia.org/wiki/Drupelet) - i.e a fleshy fruit surrounding one large stone, which contains a seed. Blackcurrants, cranberries, grapes, aubergines and chillies are all true berries (http://en.wikipedia.org/wiki/Berry), as they have lots of seeds inside a fleshy fruit. Peas, alfalfa and beans are legumes (http://en.wikipedia.org/wiki/Legumes). Peanuts are legumes too - not nuts. 'Vegetable (http://en.wikipedia.org/wiki/Vegetable)' is not a botanical term, it is just the word for anything that doesn't fit in another category. Something can be a fruit or legume in botanical terms, but can still be referred to as a vegetable in culinary terms - such as tomatoes and beans." Source: http://www.eupedia.com/forum/archive/index.php/t-21458.html

Just thinking about the definition that veg grow under the earth, and fruit above... A lot of 'fruits' are sweet, and a lot of 'vegetables' aren't. 'Fruit' generally doesn't need to be cooked, 'vegetables' generally do. Mmm...