Because their doctrine believes that their purpose is to bring children into the world, and by having kids its a celebration of the life given to them by god. Also, in all stems of christianity I believe abortion, contraception, and even condoms are not supported 100%. Abstinence believes that if you do have sex, and you get pregnant, it is your job to have the child. So basically, the goal is to populate the earth with more believers.
They like to remain faithful to their spouse and religion. I cannot think of any other reason in other terms. Maybe they juat enjoy raising children in general? Also, raising them in the same mannerism with regards to the religion could set a big factor... I'm not really sure either... I respect them either way as long as they responsibly take care ofthe children physically, emotionally and psychologically. Not a big deal.
well I heard it is becuase the more children they have the more mormans there are ... they want to take control of everyone they want us to all be morman that's why they have so many missions...get it...
i don't know about mormons personally (sorry) but it says in the bible BE FRUITFUL AND MULTIPLY so that might be why. I know that catholics don't believe in abortion but I don't know if mormons follow that too.