Why do actual workouts not work with Airplay, but previews do work? Infuriating

I wouldn't know but the current list of supported devices are

iPhone

• iPhone 6s with iOS 14.3 or later
• iPhone 7 with iOS 14.3 or later
• iPhone 8 with iOS 14.3 or later
• iPhone X, iPhone XR, iPhone XS, iPhone XS Max, with iOS 14.3 or later
• iPhone SE with iOS 14.3 or later
• iPhone 11, iPhone 11 Pro, iPhone 11 Pro Max, with iOS 14.3 or later
• iPhone 12, iPhone 12 mini, iPhone 12 Pro, iPhone 12 Pro Max, with iOS 14.3 or later

iPad

• iPad Pro with iPadOS 14.3 or later
• iPad (5th generation) or later with iPadOS 14.3 or later
• iPad mini 4 or later with iPadOS 14.3 or later
• iPad Air (3rd generation) or later with iPadOS 14.3 or later
• iPad Air 2 with iPadOS 14.3 or later

Apple TV

• Apple TV 4K with tvOS 14.3 or later
• Apple TV HD with tvOS 14.3 or later

All of them needs to be paired with an Apple Watch 3rd gen or higher.

My thoughts on this? Probably an anti-piracy measure.

If you can’t use the iPhone app to do workouts on your TV... what’s the point? This might as well be a tvOS-only app at this point. If this is an antipiracy measure it is the worst instance of hobbling a product with DRM I’ve ever seen.