Well its pretty simple. Just remove the most essential feature needed by almost all iPhone users and create a new alternative, forcing everyone to buy AirPods or the second-best alternative. If they won't upgrade soon, then planned obsolescence takes it course. Due to the AirPods being a platform and ecosystem in its self, there is less of a reason for iPhone users to settle on an alternative apart from price, which completes the lock-in.
I would expect Apple to make more out the AirPods after they force those stuck on iPhone 6S's or SE's to upgrade. Revenue-wise, it almost unfair to begin comparing with the revenues with any of those mentioned companies. It just puts things into perspective of how 'successful' the AirPods have become for Apple.
For a majority of people wireless earbuds are far superior than tangled corded headphones. Its pretty clear based on how popular in ear Bluetooth earbuds are. Not just on the iOS side either.
I would expect Apple to make more out the AirPods after they force those stuck on iPhone 6S's or SE's to upgrade. Revenue-wise, it almost unfair to begin comparing with the revenues with any of those mentioned companies. It just puts things into perspective of how 'successful' the AirPods have become for Apple.