Cities tend to situate convention centers and sports complexes in their cbds because

Because "they hope to stimulate more business for downtown restaurants, bars, and hotels".

A central business district (CBD) is the business and commercial focal point of a city. In bigger urban communities, it is frequently synonymous with the city's "monetary area". Topographically, it regularly agrees with the "downtown area" or "downtown", yet the two ideas are partitioned: numerous urban areas have a focal business locale found far from its business or social downtown area or downtown. 

It would be an example of inductive research