The standard BTX layout is it quite Intel centric that makes it unattractive for AMD motherboards, and probably less useful for Intel going forward.
Here is a picture of an
Intel DG965MQ Micro BTX motherboard .
The big heat sink next to the RAM slots is the Northbridge. The CPU socket is further from the RAM at the front of the board. The position of the RAM, CPU and Northbridge are all part of the standard, and cannot be moved. Clearly this works well for current Intel designs where the memory controller is in the north bridge, but not for current AMD designs where the memory controller is in the CPU. That is one reason why BTX AMD motherboards are very rare.
The thing is, Intel are probably realising that AMD had the right idea about putting the memory controller in the CPU, and if they adopt that design then they will face the same disadvantages with BTX as AMD have.