The competition is fierce among smartphone brands. The camera and camera features are now a critical aspect in phone marketing. More megapixels, more cameras, and better software are key features when it comes to market strategies.
R&D is expensive so establishing partnerships with other manufacturers makes sense twice: Firstly, it saves on development resources. Secondly, it validates the brand and puts a prestigious halo around it. Just look at the last crop of partnerships: Huawei & Leica, Motorola & Hasselblad and Nokia & Zeiss. (I could possibly say Sony & Sony, but that would just be funny). Now Xiaomi wants in on the camera “old money” and seeking out a partnership.