There are some contradictions in here. If you map your functionality from software (on CPU) to FPGA, your software becomes hardware. FPGA is hardware. FPGA is retargetable, but it is not programmable in the sense what SW requires. The resources are preallocated, which is the essential property of hardware.

In software you allocate and deallocate memory, which is your dynamic resource. You don't have that in HW. You can implement a memory manager in HW, but your system will not be flexible enough to be soft. Also you can synthesize your CPU on FPGA, but the performance is poor compared to a hard CPU on FPGA.

Currently FPGAs are becoming popular in accelerating software functions to offload the CPU. The most powerful FPGAs have a lot of fixed logic CPUs in them (i.e. hard macros).

You can't just say that I'll just go ahead and run my software functions as hardware. For certain type of workloads you always need software, in practice (not in theory).