Obviously you understood very little. Although most people cannot code themselves, with free software they're allowed to ask anybody who can to help them.
And these people consumers are supposed to ask are going to do a full code review for free? And let's hope these 'code reviewers' are very good, because no software company is going to code the sneaky stuff in obvious ways. Don't expect to find function spy_on_user() when looking around.
With proprietary software they face a vendor-lock-in with monopoly on changes to the product and usually to support for the product.
That's the same case for FOSS. Sure, they could find someone to write another software package so they can access their data, or they could convert it to something else, but both of these aren't free. When someone else writes your code you are at their mercy regarding changes, support and/or abandonment. Consumers, who are 99.9% of the software users, are locked in in one way or another.
And free software is not always gratis. Red Hat runs a billion dollars a year business with free software.
Yes they do - by charging for support. If you don't want to pay for their support you are free to hire your own support staff, which isn't exactly an option for consumers.