Probably once you're buying stuff that often, you have so much stuff that you forget what you already have and end up buying even more.
In other cases, I bought alternative devices instead of upgrading within the same platform (my Mac and iPhone are both 5 years old). The alternatives turned out not be compelling enough to fully switch to, but found a niche as purpose driven devices. In many cases distraction free devices.
In some cases, the super upgrade cycle was driven by a desire to finally stop carrying a microUSB cable with me when I travel.
As for the mechanical watches, yes I have too many.