The power profile of an FPGA is very different (worse) than dedicated silicon. Both the background current and cost of a gate switch. There are a lot of situations where that isn't acceptable.
True, that's definitely possible. I was giving the habitual answer (that I occasionally need to explain to a client at work) why you need to spend $2m having an ASIC made when "it's just digital logic and we got the prototype going in a month"
They usually care about at least one of - size, power, cost.