From the perspective of these lawmakers, encrypted storage is like a safe. You have the right to store records in a safe to keep them away from prying eyes, but law enforcement has the right to order you to unlock that safe if they have a warrant. You have the same right to store those same records on an encrypted device, but law enforcement has the same right to order you to decrypt that device if they have a warrant.
Since people will sometimes refuse to decrypt a device, even when ordered to do so by a court, these lawmakers want to require OEMs and service providers to maintain control of the keys when they encrypt information on a user's behalf so as to increase the chances that lawful decryption can take place.
Is this a bad policy? Quite possibly. It has certain risks and makes certain tradeoffs, like any other policy. But it is arrogant to assume that anyone who supports it must be ignorant of how encryption works.