It's a chicken and egg problem too. Toolchain friction and depth of knowledge required is one part. Ubiquity of FPGA silicon lying around in the average programmer's (and end-user's) machine is not there.
Silicon availability has recently been solved. There are FPGA dev boards available for under $50. They're low-powered but great to learn on. One, the FOMU, actually fits inside a USB type-A port.