I think the majority of the treaty is terrible, spreading laws that prop up businesses based on copyright and patents, and on balance I think that no country should adopt it.

In this one particular case, it appears to remove artificial restrictions that prevent consumers from doing business with companies they otherwise want to do business with. I'm in favor of that, whether it's "you can't block a company from providing a service to a person in country X who wants that service just because they don't store data in country X" or "you can't block a company from providing a service to a person in country X who wants that service just because the company doesn't provide an identical service to a person in country Y". Either way, you're preventing two parties who want to work with each other from doing so.

(Also, keep in mind that many of the "must store data locally" laws have less to do with protecting that data and more to do with making it available for attempted seizure.)

If the people of a given country want to refuse to use a particular service because it stores their data elsewhere, or doesn't have a local presence, or shows them a different selection than people in other countries, or any of a thousand other reasons, they can already choose to do so. But there's a huge difference between choosing not to use a service and preventing anyone else from using it.

I don't directly care about the profits of companies, large or otherwise, except to the extent those profits mean they've built something people want. I do care when people can't use a service they want because their country doesn't think they should or wants to prop up another. And I care when a company owned, operated, and staffed within one country suddenly has to worry about another country's government, rather than just what their users want.