If they tell law enforcement they can’t produce an unencrypted copy and it’s later proven that they could, the potential penalty would likely be more severe than anything they could have gained by using the data themselves. And any employee (or third party they tried to sell the data to) could rat them out—so they’d have to keep the information within a circle too small to make use of it at scale. And even if it never leaked, hackers would eventually find and exploit the backdoor, exposing its existence. And in either case they’d also have to face lawsuits from shareholders (rightly) complaining that they were never warned of the legal risk.