A breeder will breed because of the potential profit margin and they have a good blood line in a dog or bitch I haven't said all breeders but breeding in general isn't a good thing IMO.
Now why do you breed on occasions ? It will interest me to know why.
I don't know what sort of breeders you know or in what breed.
I breed when I a) am ready to bring on a new puppy b) have a bitch that is not only talented but also fulfils all the criteria of excellent temperament, excellent health test results and are the type I like. c) have others interested in puppies from my girl as the likelihood of her having a singleton for me to keep is very small. I compete (not show) with my dogs and people who like my girl show interest in a puppy from her, however, they are equally at home as pets only. Therefore, a large majority of homes are known to me, however, not all are and they are vetted very carefully. I turn some away (sadly, they will probably get one from a puppy farmer or byb but they will not get one of MY pups).
It is a huge undertaking to breed a litter well, in both time and money. While I agree with Chazz, I think some of the costs she has listed are conservative, although it will depend on area, particularly for vet fees. I could list them, but I think I may give myself a heart attack.
In a nutshell, I do it because I love my breed and if I have a really good bitch whose genes really benefit the genepool I will breed. However, it is not without a huge amount of guilt and worry too. Dogs (bitches) do not ask or need to be bred and it is not without risk - far more risky than a human pregnancy.