I think a key difference here is that the prompt is not asking you to choose between the browsers you’ve already installed, it’s asking you if you want to launch chrome or safari, and if you don’t have chrome it’s an install button to the App Store. It’s essentially just an ad, presented like a selection UI.
Properly implemented such prompts would be great though. Someone else in the thread mentioned how location search results on mobile Safari always launch Apple Maps - it would be great to have the option to choose from whatever I have installed.