Why Would my Dentist Use a Crown Instead of Veneer?

Sometimes it's just semantics - a veneer is usually just the front part of a tooth, but often needs to have the tooth preparation over the biting edge of the tooth and possibly even slightly between the teeth.  A crown is really just extending the same preparation around the inside of the tooth. If the teeth had fillings or were more damaged than anticipated then crowns would be the way to go.  Either way, discuss with your dentist.  Communicate your concern as there would have been a logical reason for the change.

Based on the information you have provided I am not sure why he would place a crown.  I would discuss your concerns with your dentist.  You may have had an issue with the enamel.  Speak to you dentist so you can have some of your answers

You have done a lot for your smile-nice job! I sometimes will do what I call a veneer / crown. I will use when i need more retention to hold the veneer, the chip is big or I also want to close space. Ask your dentist - have open communication and smile-you are almost done!

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.

Sometimes when prepping teeth we don't' see all the cracks until we are working.  Also, you may THINK it was prepped for a crown, but it is closer to a 3/4 crown or veneer.  The temporary crown/veneer may cover more tooth than the final restoration will, so that may be a factor.  Without seeing the teeth, it is hard to tell.