Why Would my Dentist Use a Crown Instead of Veneer?

Here are some facts to consider why your dentist may have chosen to fabricate a porcelain crown instead of a porcelain veneer:
The choice between a porcelain veneer or porcelain crown generally depends on the condition of the underlying tooth structure, the design objectives and amount of tooth preparation needed.
Porcelain veneers are usually placed on teeth that have a greater amount of healthy tooth structure whereas porcelain crowns are placed on teeth that require more support or have less remaining healthy tooth structure.
Porcelain veneers require less reduction of tooth structure and usually cover the outside or facial surface of the tooth and wrap over the edge of the tooth whereas porcelain crowns are generally a full coverage preparation and design wrapping/covering  the entire tooth.
Many times a combination of veneers and crowns can be used to create a desired aesthetic result.

First of all, why don't you ask your dentist! He should be able to provide you with an answer. There might not have been enough enamel on the tooth to support a Veneer.