The big barrier is that the FPGA design tools from the FPGA companies are full of bugs that you spend an inordinate amount of time trying to work around. Some open source tools like Yosys have emerged. So far they're limited to the ICE-40 FPGAs from Lattice and a few older Xilinx parts.

Expensive hardware FPGAs are significantly more expensive than microcontrollers, which can be sourced at a fraction of the cost, regardless of production scale. Since they're application-specific, ASICs are expensive to produce in small quantities but are far more cost-effective than FPGAs in mass production.

The process of choosing an FPGA is like any other decision-making process in our life. First you look inside to collect all the requirements for your project, and then you weigh your requirements by importance. For example, if the most important issue is cost, that might make some FPGAs more appealing than others.