Yesterday, Microsoft finally began the process of rolling out Windows 10 Mobile in an official capacity for older Windows Phone 8.1 devices. In many ways, the Windows 10 Mobile era has now started.
Despite 18 phone models (see the full list here) being eligible for the upgrade there are plenty of older Lumias not getting the update too including any phone with 512 MB of RAM. Compared to Android Microsoft is another league (don't take my word, see what Hildenbrand thinks about the Windows 10 Mobile upgrade process at Android Central).
One of those phones not getting the update is the Nokia Lumia 1020, which was released in the summer of 2013. However, the reason for the Lumia 1020 not getting the update is unrelated to it being a nearly three-year-old phone. Instead, it is about stability, performance, and user feedback. Microsoft's Gabriel Aul responded to a user about the decision:
Lesson learned? Microsoft's feedback app for the Insider program is not a feel good tool to make everyone think Microsoft is listening. Instead, the company is using the data to make real decisions such as not pushing official Lumia 1020 Windows 10 upgrades. Phones that had bad performance with the Insider program and low recommendations get cut. Instead, Microsoft is prioritizing a quality experience.
There is little reason to think the same criteria were not applied to other older Lumias as well.
In other words, if you don't like some of the choices or directions Microsoft is making here you can lay the "blame" at your fellow Windows Phone users who evidently gave very honest feedback about the Insider experience.
Should three-year-old phones be expected to get Windows 10 Mobile? There is room for debate there, but hopefully, it is now clear that Microsoft is not arbitrarily picking phones, and, at least, some of their decisions about this matter are based on real telemetry and user feedback.