The answer I believe is: because this all used to be much harder, and you had to rely on your engineers to pull you through some tough moments. I'm afraid this is becoming less true over time. The pendulum is swinging back from technical implementation, back through design, and the power is returning to sales and marketing, IMO.
HOWEVER, people who can engineer marketing outcomes... those guys will keep the power.
TLDR; Hie thee thither to up-market positions ye men of valor!