Privacy policies can change at any time, but that's not the only problem. Companies that hold your private data can be hacked. They can be acquired by new owner

Privacy policies can change at any time, but that's not the only problem. Companies that hold your private data can be hacked. They can be acquired by new owners who don't care about privacy. Even if you trust a company with your private data, and even if you are fully informed about the data that they collect and what they use it for, you will have no control over what happens to that data eventually.