> Imagine onboarding for Netflix including a pleasantly designed screen saying "Before you can use Netflix, you must Enable Third-party Stores. Go to Settings > Privacy..."

From Netflix' perspective that still adds considerable UX friction, and some percentage of potential customers will drop off.

At what percentage cut is it better for them to just stay in the Apple store? 10%? 5%? 2%? At any of those rates Apple still makes boatloads of money.