In my opinion, it's simple. Cost. 747's are costly machines to keep & maintain, although I'm no expert in operating costs of specific aircraft. Even though they bring an aura of "prestige" to companies, maybe airlines today are more inclined to use planes that don't need to be filled with so many people to earn profits on them. Afterall, there is competition out there. I do not think that they will just completely dissapear. They are still big with Asian airlines. But this is just my opinion.
My internet was not shut down, the internet has shut me down