Because I'd rather have an American tech company own all of my personal and sensitive data than an antagonistic, Russia/North Korea/Iran-aligned country that we could potentially go to war with within the next century. In the United States, tech companies are privately-owned and largely answer to themselves, only really answering to the United States when they're up to some shady shit - if that. In China, companies are effectively treated as a branch of the CCP at the end of the day. They aren't independent companies in the traditional sense. If the CCP wants information, these companies will gladly hand it over, because it would be against the law not to. You can't point at Apple and say "this company IS the United States government", but you can do that to a Chinese-owned company and be right about it.

The terrorism implications with the latter are scary as shit. It's not just browsing history and harmless data, it's the profile that you can put together of people using that data to allow you to eventually connect the dots to the truly dangerous information, like social security numbers, passwords, medical data, financial information, et cetera. If you have the personal information of every citizen of a foreign country, and you're able to build enough of a profile off of provided information that you can do some truly dangerous things with it, then you effectively have that country by the balls - it just becomes a matter of when/if you squeeze.