We already had two (I don't remember the order, but they were called Privacy Shield and Safe Harbour) and somehow US and US companies "forgot" to upheld their part in any meaningiful way, so there's some mistrust on the whole idea at the moment...
The EU parliament have the people in mind, so they don't think it works and drove the GDPR. The EU courts look at the law and see it's not possible to create contracts, so shot down Safe Harbour and Privacy Shields. The EU courts say standard clauses could work in principle, but see above.