No. You have an option with AA as most airlines are just keeping it simple.I think point is to sell you 2 separate baggage classes; If I have to pack only dive equipment to sport luggage, I have to buy another baggage that is also 20kg for the rest of my personal stuff.
You can simply pack everything in one or two bags and pay accordingly.
My checked bag with full scuba kit is under 20kg and there is no reason for me to pay for two bags. Scuba equipment is pretty tough and I never had anything broken in my soft checked bag.