Iran is a signatory to the Nuclear Nonproliferation Treaty. According to the treaty, they agreed to not pursue nuclear weapons and to allow IAEA oversight.
Making it difficult for the IAEA to provide oversight is enough of a treaty violation, and that goes double when there is credible evidence that unauthorized enrichment was occurring.
Why do non-US companies care about US foreign policy goals? EU companies can benefit from doing business with Iran, on the other hand using US based SaaS only makes them hostages of the US government and provides zero additional benefit. It would seem that using US based SaaS is simply bad risk management on the buyer's part.
