I work at an optometrist's office. The reason there is a seperate charge for a contact lens fitting is that a contact lens fitting is not part of a routine eye exam. Not every person wears contact lenses. Most insurance companies do not pay for a contact lens fitting as contacts are considered cosmetic.
And a fitting must be done and charged each year in most states as it is a state law. The shape of your eye can change as well as the prescription, so it is really beneficial to the patient to have a new fitting each year.
I know it's a pain to pay that each year even if there's no change with the brand or size of the lenses, but it must be done!
Not only may the shape of the eye change and the prescription change, but the patient may have undiagnosed infection, ocular surface disease, dry eye, or other problems. The optometrist must make absolutely sure there are no problems before allowing a patient to continue wearing contact lenses. A referral to an ophthalmologist for treatment may be necessary.
An annual exam for contact "fitting" is not routine and is not just "fitting." If the provider is not providing a thorough exam, find another provider. Your vision may depend on it.