Because even if your phone only breaks every 5 years on average do you want to get a new 5 year old phone because your last one died right before the refresh cycle? Having regular releases means that when you do get the phone you have a relatively up-to-date device with latest hardware improvements. You don't need to upgrade yearly because they release a new phone yearly.
You probably don't, as your current phone ought to last for years. But hardware manufacturers, like software developers, benefit from faster release cycles.
