Selling Tesla to buy SpaceX would incur a taxable event, and holders would need to pay capital gains, decreasing the size of their investment. If SpaceX acquire

Selling Tesla to buy SpaceX would incur a taxable event, and holders would need to pay capital gains, decreasing the size of their investment. If SpaceX acquires Tesla, there's no taxable event. Also, part of this is their own self-delusion to discourage each other from selling to buy the shiner new Elon project.