Because if they were actually slated and have now pulled out, the organizers best bet would be to rent the floor space out to a soccer league to try to recoup their costs.
That list is broken into three groups
Vendors Pulled Out (207)
businesses who were going to be exhibiting at the show who have now pulled out
Speaker / Celebrites Pulled Out (32)
people who were going to be exhibiting/speaking at the show who have now pulled out
Other Boycott Supporters (39)
people and businesses who are sympathetic to the second amendment who are letting their customers and followers know what a bunch of anti-american vermin the organizers are