The assumptions are that

* "better models" will remain so signficantly more profitable for firms that have access to them that that they're effectively a "must have" for big orgs, rather than a grossly overpriced marginal gain

* said better models will only be attainable by orgs in US jurisdiction, rather than by foreign alternatives that come to be either independently or through a legally clever "cleaving" of a US-jurisdiction business interest that wants access to an eager international market

If either of those are wrong, restricting Anthropic et al to only sell to the domestic market is effectively a poison pill that makes it much harder for them to meet growth and profitability objectives and could see them lose their market-leading position sooner and more thoroughly than if they retained access to a larger market and had more flexibility.