Whatever they release is NOT stock or close to stock Android btw. They release their own customised (bloated) Android which is why most budget phones with 1 GB or less RAM lag!
Stock Android or near to stock Android performance is noticeably better than these OEM customised (bloated) Androids, especially on budget phones.
Your Grand Prime can run twice better on Stock Android than its very own bloated Rom.
In simple words,
Android One = budget phones + close to stock Android + fast track latest updates for ~2 years.
Well known OEMs don't provide these two last things, except for very few. Of course, they can update it anytime they want, even on their own, without being a part of Android One. Its upto OEM manufacturers to decide, but most of them don't do that on budget phones.
Like you said, Motorola offers something similar without being a part of Android One. It offers close to stock Android and fast track latest updates, even on budget phones. A budget phone like Moto G is going faster than flagship Galaxy S4 and S5 in terms of latest updates.
Even Huawei is doing great, Android M is coming for Honor 4C and 4X.
My point is, the well known brands should also offer close to stock Android and fast track latest updates for some budget phones. They CAN do it, but the problem is, they DON'T do it.
