Why hot pack when raw pack is just as fast?
According to Pick Your Own, the main reason is that in raw packing, more air is introduced into the jar.  This may lead to discoloration over time, which is an aesthetic issue, rather than a safety issue.

Regarding hot packing, they describe the benefits:


  This practice helps to remove air from food tissues, shrinks food,
  helps keep the food from floating in the jars, increases vacuum in
  sealed jars, and improves shelf life. Preshrinking food also permits
  filling more food into each jar.


They provide the following guidelines regarding which method to use:


  
  Use the hot-pack method, especially with acid foods to be processed in boiling water rather than a pressure canning method.
  The Raw pack method is fine for pickles and for vegetables to be processed in a pressure canner.
  


See also:  National Center for Home Preservation describing the differences, benefits, and reasoning in great detail.