While I don't touch anything Meta (formerly Facebook) at any time, what is the explicit route of data gathering here?

From what I understand, these companies willingly give user data to Facebook, which then utilizes the data to: Use the provided information to match your Facebook user id with the other companies' user id, so it can understand when you made an activity in the other companies' sites, games etc. and show you stuff (ads only if you are naive, or propaganda through engineered post and ad visibility jf know at least about Cambridge Analytica) about it when you are in Facebook.

Is this the route user data follows and is utilized? If so, shouldn't these mentioned other companies including Facebook's and whatnot's 3rd party tracking pixels n their own domains, and also sharing your data to themselves directly be the focus of privacy concerns as they "leak" your user data? Doesn't the most of the blame fall on these other companies, or does the implied blame here that user data transfer is mutual and Facebook forwards these user data from company A to company B in the list, as well?