Because I keep using their stuff, quite proactively, and productively, and when it breaks and its Apples fault, I can go back to them and get a new one, no questions asked, and get back on with using the thing.
vendor lock-in, hard to use anything else. Addicted to Mac ecosystem, lots of data in iCloud, lots of purchased music, videos and apps from their stores? :P
Literally, none of the above in my case. I don't use iCloud, no purchased music or videos, and 'brew' is my app-store. I could switch to Linux in a heartbeat, and probably will, with my next hardware upgrade. But in the meantime, Apple keep me on their platform by providing superlative replacement service.
If a device I buy fails for what I consider to be a design or manufacturing mistake, I'll be wary of the company. If it happens again, I won't buy more of their stuff.