At the latest Q&A Elon said they were not focusing on the energy side of the business because it would require them to not make a number of cars due to being limited on battery / inverter supply.

This becomes exponentially harder as they add more and more power hungry vehicles to their lineup (see Cybertruck / Semi) and market more Mega/Gigapacks to grid operators.

It makes sense for Tesla to try to get as many batteries as possible from as many sources as possible.