Well, with furniture and backpack companies, the tolerance (or "forgiveness") for user error is a lot higher. If you accidentally drop your backpack, it doesn't have a screen or anything that shatters and requires a $150 part replacement. You can't even drop furniture in day-to-day use, really. Moreover, your backpack doesn't have a battery or anything that slowly but surely degrades over time anyways with a meager five-year lifespan.
I can't imagine too many ways that a backpack or piece of furniture can become accidentally damaged by "user error." Remember, so many people try to misrepresent their own mistakes (perhaps because they didn't understand what happened or they didn't realize it was their own fault) as product defects that the phone manufacturers all had to add things like internal liquid sensors to their devices.
On another note, many of my non-technical friends conflate Android OS software problems with device defects (e.g. "my phone died" actually meant that they had 300 running processes because they never learned how to close running apps on Android -- which to be fair is a PRETTY buried feature that doesn't lend itself well to user discovery; the number of people I see that don't realize they have to manually close apps on their Android phone is shocking). It's probably the reason there are so many ways to buy "refurbished" devices.
Needless to say, if Apple or Google started honoring a lifetime warranty, they'd lose a lot of money pretty quickly.