The answer to your first question is because of your second question. The channels that are part of the sports package are in the higher channel numbers.Does anyone know why the NBA channel is not in the 212-220 grouping and why you have to have the Sports Pack to have it? Seems out of place to me.
As to why it is part of the sports pack and not a lower tier package...I don't know. Probably has to do with the contract between D and the NBA.