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Qualcomm is a fabless company, as is Nvidia.
Being fabless, and successful, comes with a management chain that knows how to effectively and efficiently manage a productization chain that is not capital intensive.
Owning a fab is a capital intensive operation. Qualcomm's management would not know how to effectively manage an asset such as AMD. Neither would Nvidia which is partly why past rumors of Nvidia acquiring AMD were equally pointless speculation.
The second reason why Qualcomm would likely not bother acquiring AMD is the x86 license restrictions in place. Should any company acquire AMD the existing x86 license with Intel would be nullified per the stipulations in the contract.
The third reason why Qualcomm would likely not bother acquiring AMD is that Qualcomm stands to gain very little by doing so. AMD's technology does not enable Qualcomm to differentiate any given product line so much so that it makes sense to invest $5B into the product line's future by acquiring AMD.
The prospects of Qualcomm acquiring AMD is akin to Apple acquiring Micron for the sake of owning a company that manufactures the NAND memory Apple uses in their iPods and iPhones.