He actually doesn't own both companies. He largely owns X which is a private entity. He owns ~20% of Tesla, and the rest is owned by other shareholders. As a c

He actually doesn't own both companies. He largely owns X which is a private entity. He owns ~20% of Tesla, and the rest is owned by other shareholders. As a company officer he has a fiduciary duty to act in the interests of all Tesla shareholders, and any sales or deals to other entities he has in an interest in pose a conflict. That conflict can often be mitigated by oversight or deferral of decision making to parties that don't hold the conflict such as other board members or corporate officers.