To answer the question quickly? Some of us are forced by the vendors themselves, because the OS's and apps become outdated. As an example, I strongly resisted having a smartphone until I have been given an old Samsung GT5830. I like some of it's functions but there is one major problem. The OS is not upgradable, on some occasions I cannot run any google updates, because it's complaing my browser it out of date, etc. It's the "out of date" and "being unable to upgrade" forced upon us my the like of Google, MS and others.
With all the old computers I have at home Linux is the only option and I also collect every free outdated laptop my company throws to the bin. Linux keeps me going and up to date. Forget Windows and MS who are the main culprits forcing all those upgrades to occur. It's staggering how much and how quickly computers are considered expired in companies. That includes OS versions of every type.
As for my new gadget? It's old but as long as it works I'll keep it. I only use it as a pay-as-you-go phone and to connect at home to my WI-FI when my computers are switched off. It does the job, that's it. When I look at the priced people play on a monthly basis for having a fully equiped device I doubt there is any sense in that. Although I just looked up a rather good option for paying for a network connection on the go when I need it, check this:
https: / / www <dot> giffgaff <dot> com/goodybags/10pound-goodybag
No need to pay a hefty fee every month.
Pete