One reason the letter exists in the first place is because the current leaders in AI would love to pull the ladder up behind them. That’s why they have fostered much of the doom mongering around the technology, which has lead to so many asking for a pause. A pause during which they can solidify their own positions and cut off competition by skewing AI regulation in their favour.
Some of the signatories of the letter are already openly calling for open source AI to be outright banned, because apparently only corporations like OpenAI can be trusted with it.