Companies and governments are still punch-drunk on data, and have believed the wildest of promises on how valuable that data is. The research showing that more data isn't necessarily better.
Many organizations are still downplaying the risks. Some simply don't realize just how damaging a data breach would be. Some believe they can completely protect themselves against a data breach, or at least that their legal and public relations teams can minimize the damage if they fail. And while there's certainly a lot that companies can do technically to better secure the data they hold about all of us, there's no better security than deleting the data.
Some organizations understand both the first two reasons and are saving the data anyway. The culture of venture-capital-funded start-up companies is one of extreme risk taking. These are companies that are always running out of money, that always know their impending death date. They are so far from profitability that their only hope for surviving is to get even more money, which means they need to demonstrate rapid growth or increasing value. This motivates those companies to take risks that larger, more established, companies would never take. They might take extreme chances with our data, even flout regulations, because they literally have nothing to lose. And often, the most profitable business models are the most risky and dangerous ones.
Interesting article about the risk of keeping unneeded data.