There's the matter of material concerns, but there's also the matter of consent. These companies have presented their products as being functionally identical to doing things in house, but with the advantage of not having to. Their whole selling point is privacy, compliance, security, etc.
It's like when people found out that Ring/Alexa staff were viewing their recordings and got upset. Even if they make super sure not to commit any further violations with their access, the act of consuming and making use of my data is a violation in of itself. It violates my privacy, and my ownership of my data. Even if my data can't be retrieved from the product you use it to make, it still feels icky that you changed the terms of our deal without my permission, and took advantage of our relationship to make extra money off of stuff that is fundamentally mine, and I have no recourse.
If my landlord surveilled my apartment and sold the footage on PPV but only in China, the material consequences to my quality of life would be negligible. There's virtually no way that any of the people watching the footage would ever contact me or interact with me in any way, especially if they did it with all of their tenants and randomized the footage such that it's hard to track one specific person. But it would still feel super weird and bad, and it would still be a violation of our relationship.