This is only really true of marketing campaigns, and even then only in some instances. In certain kinds of marketing (e.g. direct campaigns), there may be downs

This is only really true of marketing campaigns, and even then only in some instances. In certain kinds of marketing (e.g. direct campaigns), there may be downside risks to casting too wide a net beyond just cost vs profit. It's also important to understand that these data aren't just used for shotgun marketing campaigns, they're also used in highly targeted applications. For example, if you give a company a small amount of information about yourself, for example through a insurance or financial services "estimate" page, that company has very good reasons for wanting as much (and as accurate) data about you as possible. The two biggest reasons are: 1. If they're smart, they're running models to associate those and other things with purchasing behavior. Notwithstanding the fact that they need to stay on top of the model's accuracy, having information about you that is too incomplete or too inaccurate can really fuck up their shit. 2. In domains where customers are extremely profitable (again, e.g. insurance and financial services), it can likewise be extremely expensive to acquire the data needed for robust modeling, even dirty data. In both of these cases, they do very much care "about having data about 'you' in particular".