I always wonder if they could've spend the timer better by investigating into Java-Graal. Or rewriting their Stack into X. I mean facebook is probably already p

I always wonder if they could've spend the timer better by investigating into Java-Graal. Or rewriting their Stack into X. I mean facebook is probably already polyglott, so... why they still embrace PHP that much, when they have a performance concern? or why do they spend so much in creating their own jit, when they could've gone a way cheaper route in the past. is it so important to control their own stack?