Hey Leroy,
Yep, there are a few reasons for that. When I started MrMobile I decided to broaden my coverage to include mobile technology other than phones (cars, computers, mobile work solutions, trains, etc). Covering those other categories cuts into the total time I have to dedicate to making videos, so some culling of the list had to happen. Also, I'm targeting mainly a North American audience with most of MrMobile's content, and ASUS/Lenovo/Xiaomi/Meizu/Oppo/etc usually just don't sell enough here to make the cut.
But I do try to cover exceptional devices when I have the opportunity (and when they're truly deserving of it). The Mi Mix was a recent example, and I plan to cover the Runcible whenever it finally lands.