Apple Wallet is the stickiest of sticky things
Now, with its foundation being laid over the last decade, Apple is putting its foot on the accelerator to make Apple Wallet inescapable, for better or worse. Apps will soon be able to get ID and age verification (enabled by the rollout of digital driver's licenses); flying and other governmental checkpoints should be faster; and a pay-later service will be available. These things are all being enabled to make Apple Wallet on iPhone a trusted and important part of daily life... More here.
iMessage was for a long time considered to be the sticky that kept people using the iPhone and by association Macs, iPads etc, but it is so much more than that. I use Apple Pay for 99% of payments and have done for a long time, and truth be told I cannot imagine using anything else.
I could move away from Apple Music to Spotify or another competitor, I don't use Apple Books, Apple Arcade is OK and I don't currently use an Apple Watch, but there are some things that I would struggle to give up.
iCloud is everywhere for me (photos in particular). Perhaps it shouldn't be, but it is.
Apple Pay is essential to me.
Messages would be difficult to 'downgrade' from.
Ultimately I just prefer iOS and macOS to the competition for so many reasons, far too many to list, but those particularly sticky areas really are the glue that stop me from even looking elsewhere. That's good and worrying at the same time...