GPA Weight is not necessarily looking at the Alternate Weight, it is a separate item and depending on what the school is looking to do they can set the score with the Alternate weight formula or not.

In the case of Simple GPA, the weight does not add a bump to the score, but with weighted GPA it does depending on your calculation.

Alternate weight is another way to pull an average and if the school changes the calculation but doesn't want it to affect what is already in the system, it can be added to alternate weight in order to add a new weight. Alternate weight is not required.