That works fine if the company itself stores the data, but becomes difficult to enforce when 3rd parties store the data. Imagine a company with an EU presence stores it's EU data in US, with a hypothetical cloud provider that doesn't have an EU presence.

The company would need to have a DPA with it's cloud provider. That cloud provider technically would also need a corresponding DPA with any 3rd parties that they themselves use, except without an EU presence that is hard to enforce.

In this case where there is one hop you could argue that it's the companies responsibility to ensure that their service providers are operating in compliance. Imagine the same scenario, but with one, two or more middlemen and the whole thing becomes an unenforceable mess of jurisdictions for the company to do meaningful due diligence on their service providers.

It's much easier for the EU to say EU data has to be stored in the EU, and know that any party touching the data is likely to be in compliance, and significantly easier to investigate if they are not.