The other reasons are: power, power, power. FPGAs use orders of magnitude more power to accomplish the same task as an ASIC since you're doing lookups of bits

The other reasons are: power, power, power. FPGAs use orders of magnitude more power to accomplish the same task as an ASIC since you're doing lookups of bits in SRAM tables instead of directly implementing the logic functions using transistors. This is great while prototyping, but less useful in a mass produced device where virtually all functions are fixed at time of product release.