Why is a tomato considered a fruit?

Botanically speaking, anything that bears seeds is a fruit. The fruit forms
from the reproductive part of the plant, i.e., the flower. The ovary of the
flower becomes the fruit and inside the seeds form. So a tomato comes from
the flower and inside are the seeds. So it is a fruit. A nut is a seed and
the shell is the fruit. Anything from a part of the plant that is not the
flower is vegetative, i.e., does not reproduce. So leaves, stems and roots
are vegetables. So lettuce, carrots and potatoes are vegetables.