Because there are different kinds at different dosages, not every type works the same for everyone. They can also have some serious side effects. (I had a friend who had a stroke caused by her birth control pills.) It also helps regulate people taking them incorrectly. They effect the hormones in your body which if used incorrectly (like someone who skips the week of the placebos) can really mess your body up. They are not something to be dealt with lightly.
It may cause side effects, it's important to choose birth control method carefully. Besides, only specialist can help you find the most suitable option for you. Personally, I use Implant Birth Control and I have to say I am definitely satisfied with its effectivity without any side effects. But it's individual.
Birth control pills effect the body, they aren’t candy. The medical professional wants to make sure you are healthy enough to be on a birth control pill which may also include a physical exam, as well as assess which brand/formula of birth control pill will work best for you. Birth control pills are not “one size fits all” like band-aids.