At the physical level: capacitors age and blow up, batteries stop charging.
At the efficiency level: when the work you want to do uses more energy on an older platform than on a newer platform.
At the convenience level: when the newer device is so convenient you never use the old device, telephone versus desktop as an example for most people.
After reliability level: if you’re constantly replacing things on a unit, where it becomes your part-time job.
The longest used devices tend to be embedded industrial devices. They have a job they keep doing that job and until they break they’re going to do that job forever. And that’s application specific computing.
Most home users are general computer users, so they have a mix of different requirements, support and use cases. I for one still use a 10-year-old laptop. And it’s totally fine.