>I'm sure the throne is big enough for more than one person.

You underestimate the scale of resentment and competition between elites. If it were simple a matter of elites always preferring cooperation so they can share a seat at the table, then Musk's ousting from OpenAI wouldn't make sense (they lose their biggest investor), Amodei's departure (they leave the closest company to AGI to start their own firm), the fact that OpenAI was created in the first place was based on a fear of Google holding the keys to AGI, Ilya still left Google though on to join a startup, and then left that same startup (OpenAI) to start his own firm.

The rational decision at all those points would be to stay with the incumbent and share the monopolized glory. At each point, personal and idealogical differences dominated in decision making. I feel such will persist as these companies vie for their slice of the lightcone.

You are underestimating their opportunism