Developers want a solution, not cells. It’s why Tesla’s Megapack solution is so popular, and they have a years long pipeline even at 80GWh/year of manufacturing capacity (split equally between California and China). Autobidder is also state of the art for orchestrating the assets for developers.
With that said, BYD has a strong offering and recently landed a large contract (12.5 GWh) in Saudi Arabia.
Where's the value add in buying a Tesla battery instead of just getting one from one of their suppliers?