the AMD-FX-Processor (AM3+) is the successor of the Amd Athlon II / Phenom II (AM3).
AMD was AFAIK early to the market with a quad-channel Memory-Interface for the Operton for the Interlagos-CPUs, introduced to the market in November 2011 (Intel Westmere in 2010).
Intel then introduced Triple-/Quad-Channel-Memory to the Desktop-Market in January 2011 (Sandy Bridge).
The AMD FX-Processor was introduced to the Market in November 2011 with up to 8 Cores and higher Clock-Speeds compared to the previous generation (Phenom). A revised Version of the FX-Processor was introduced to the market in Oktober 2012 (Vishera), in 2013 extremely high clocked Versions of the FX-Processors (up to 5 GHz) were released.
The Quad-Channel-Memory-Interface was never introduced to the AMD-FX-Processor, even though it is technically available since 2011 for the Server-Variants.
When I run an 8-Core-Processor, especially with very high clock-rates (4 GHz+), the thruput in many applications will be limited by the Memory-Interface (especially when all 8 Cores are used in parallel).
AMD should have been aware, that AMD will not be competetive against Intel (as they offer Quad-Core-Memory-Interface) for their Desktop-Processors since 2011 (the introduction of Sandy-Bridge-Processor).
So why was this never added to the AMD-FX-Processor?
Makes no technical sense for me (and is one reason, why I will not buy an AMD-FX Processor).