Why only US residents can participate to some IPOs? (opens in new tab)

I read these kinds of disclaimers regarding IPOs in US markets: To participate in the [company name] IPO through [broker name], you do not need a minimum account balance, but you must be a U.S. resident with an active, eligible brokerage or IRA account and a completed Investor Profile. [broker name] acts as part of the [bank name] underwriter network. Why only US residents can participate to some IPOs in the US?