Why does the occupation I had during the marriage have anything to do with determining spousal support?

Your occupation matters because it is indicative of the standard of living you had during the marriage, and it is also a good indicator of the standard of living you will have after the marriage. If you are to be the recipient of spousal support, your occupation will determine the extent to which you can support yourself. This is a necessary variable of the support equation.

If you are the payor, your occupation will determine how much you can pay or afford while maintaining your own lifestyle.