For years the government used cell phone data to track locations without it being known. Why wouldn't they use a more reliable way of doing it? Is there any reason to NOT suspect it?

My question was about FindMy in particular as opposed to other ways of obtaining the data.

Yes. The NSA is collecting any data it can get access to.

Would you suspect a known burglar of wanting to rob your house? Well the NSA violated privacy of hundreds of millions of people. They deserve all the suspicion and no forgiveness.