For one reason, because the data lives on forever, and these companies merge or go out of business eventually, at which point the data ends up in the hands of s

For one reason, because the data lives on forever, and these companies merge or go out of business eventually, at which point the data ends up in the hands of someone else. Data is also shared with data brokers (Acxiom and the like) which collect unknown quantities of data about you, linked to your actual identity. That data can then affect whether you get a loan or a job. Most importantly, we don't know what's done with the data and have no control should we want it to be forgotten.