IT industry manufacturers scope for machines for a purpose - to run Windows and Office or to run CAD or Gaming or whatever. They generally scope most of their products with an expected life cycle of 2 years running the current generation software for that purpose (including expected updates and etc released within 2 years of the hardware being built) well. 3 years adequately.

After that, almost nobody offers warranty on a portable device. They're likely to have been beaten to crap and they're likely to run poorly with updates so the maintenance and support costs on warranty gets too high. Extended warranty is a gamble on people losing their warranty information, upgrading to other tech and leaving their warranty covered device on a shelf, or buying a device that exceeds their requirements and then under utilizing it. If you try and extend that warranty - users piss and moan about the fact that it's 'broken' when it doesn't perform as well as a new device after 5 years of software updates - often entirely new OS releases and massively increased component demand. They want a new free device because their old one hasn't magically gotten faster as they've expected it to do more.

Most hardware vendors would be perfectly happy with a slower development and release cycle - they'd increase prices to go with it of course - but they'd be much happier to have more time to work on their product releases. But software expectations on hardware continue to climb and users demand that their devices support new software requirements. So Hardware vendors have to keep up their release cycle to remain in the market.

The annual, or biannual replacement cycle is a byproduct of a culture and a market that demands continuous improvement.