Why can't someone exchange money for a service they find valuable? As I understand it, that has long been a common practice.
[lifts hand up] Uh-uh, me, pick me: because most consumers have been trained and conditioned by corporations that they only pay for the HW, the thing that they can feel and resell, and that the SW running on it should come for free and always be free despite SW updates being a continuous effort that costs money.
Most consumers can't put a value on SW ownership, unless that SW is a video-game on a disc in their hand. Thanks to Google, Youtube, etc, we've grown to expect that everything digital of value should be free even though it's not. So ads it is.
It's also more convenient for the consumer to have a one and done payment.
The only thing I wish is if there was a monthly maintenance package when my devices get older so I can keep getting updates that keep my device running fast, secure, and can maintain some form compatibility with most apps.
Then it became free.
When you got a computer with Windows 8 you would get 8.1 and 10 for free. 11 if you have the right TPM / chip (doubtful). Same with Windows 10 to Windows 11, provided you meet the specs. Same with Mac OS (not versed enough to list the versions).
I believe Apple started this yearly iOS update (and with that a more rapid deprecation).
I don't think people would want to spend $1,200 on a phone knowing they have to pay each year for a software upgrade. They also would not spend $1,200 on a phone knowing that next year you have to BUY a new one to get the latest software.
And in Apples mind all of this is fine. iOS has the highest adoption of the last iOS version. So in terms of non-security bugfixes they can focus on the last version. Only security fixes might warrant an update for an n-1 version of iOS.
Yet, security updates aren't "free". I'd guess that keeping an OS secure is probably more expensive than developing new features. That part gets tricky.
Also, supporting 5+ year old hardware gets harder since that hardware stops getting made and the new stuff gets more and more different.