This is just run-of-the-mill rent seeking behavior.

A huge chunk of their revenue comes from US-based enterprise customers. Earlier this year, in an effort to become profitable, they tried raising their rates. Those enterprise customers responded, in part, by ramping up efforts to migrate to open weight models. If those efforts are successful then OpenAI and Anthropic will lose their one remaining plausible path to profitability. The US banning open weight models arguably keeps that path open. I don't personally buy that story, but I do believe hedge funds and institutional investors would. That could be all that's needed for a successful IPO.

As for cybersecurity implications, long term impact on domestic AI industry or the US tech industry more broadly, geopolitics, etc., I don't think OpenAI's or Anthropic's leaders are any more worried about that than your average termite is about the structural integrity of the house it's eating.