The press and hold for 10 seconds should stay on indefinitely.
Unfortunately it doesn't. Here's what Cadillac said: "After looking into your owner's manual, while it does mention the vehicle having a Retained Accessory Power feature, it also states that the Infotainment system can only be used up to 10 minutes after the engine is turned off. The main reason this shuts off after this time is to conserve the power of the battery. The only way you can have the radio still running while in park is if the engine is still on. For more information on this, you can go to page 195 of your owner's manual where it will describe more about this feature."
I think Cadillac and other OEMs are getting hypersensitive about battery drain. I do work for some of their Tier 1 and Tier 2 suppliers, and their marketing messaging to the OEMs increasingly plays up how their tech won't cause a battery to go dead when a vehicle sits in airport parking for a week.
An example is next-gen key fob systems that can determine the driver's direction when approaching a vehicle so they know whether to pop the trunk or hatch. This eliminates the need for a sensor under the bumper to detect a foot, but constantly listening for a fob can drain the battery . . . or so the story goes. I don't see how it's more of battery suck than the foot sensor.