The performance of soft cores are significantly lower than hard cores.
Xilinx already has a RISC soft core in their MicroBlaze architecture so they don't have a pressing need for a low power, reasonable performance RISC soft core. Ref: https://en.wikipedia.org/wiki/MicroBlaze
AMD has high performance CPUs being fabbed by TSMC (same foundry as Xilinx), so (theoretically) AMD CPUs can be grafted onto the Xilinx FPGA as a hard core.
With AMD and the MicroBlaze, they have the high performance and low power processor spectrum covered with no need for 3rd party licensing costs.
Xilinx already has a RISC soft core in their MicroBlaze architecture so they don't have a pressing need for a low power, reasonable performance RISC soft core. Ref: https://en.wikipedia.org/wiki/MicroBlaze
AMD has high performance CPUs being fabbed by TSMC (same foundry as Xilinx), so (theoretically) AMD CPUs can be grafted onto the Xilinx FPGA as a hard core.
With AMD and the MicroBlaze, they have the high performance and low power processor spectrum covered with no need for 3rd party licensing costs.