What you're describing is "revealed preferences theory", and it requires a truly free set of choices—essentially, when looking at it in relation to companies like Google, it relies on "free market theory", the kind that only works with a spherical market in a frictionless vacuum.
People "have decided" this because they're not given good choices, they're not well-informed about what their data is going to be used for, and their real buying power has been going down for decades so they don't have the disposable funds to put toward the much more expensive options that would allow them to retain their privacy (even in the rare cases where such options still exist).
People "have decided" this because they're not given good choices, they're not well-informed about what their data is going to be used for, and their real buying power has been going down for decades so they don't have the disposable funds to put toward the much more expensive options that would allow them to retain their privacy (even in the rare cases where such options still exist).