Name a company that gives security updates to 15 year old tablets.
I wish they did, but this is hardly just an Apple problem. The only reason I bring this up is because people very quickly dunk on Apple without thinking about the fact that we need more access to all of our hardware in order to increase the longevity for those who want to.
Frankly I find iPads work longer on average than most other tablets. Purely anecdotal though.
The other elephant in the room is that most people don’t want to use 15 yr old tablets. I know I don’t want to edit video on 15 yr old desktops, even though they were perfectly capable of editing 15 years ago. But not current videos. Just like 15 year old tablets will not be able to readily stream or display a lot of modern content correctly.