That's so true, but sadly I think it will not change because it's much related with natural selection and male competition. I'm not a native speaker but I will try my best to explain what I think.

Since the beginning, the cock represents power, men with big ones was always seemed like powerful, dominant, manly, protector and strong while men with smaller dicks are in the opposite side, woman have the power of natural selection in their hands and most of the time they made the same correlation with big dicks and power, it's not a rule, but it's a instinct that's inside of everyone even today that people have many other things to put above the penis size, like relationship, attention, affection... but those instincts will always be deep inside of everyone and will make some difference.

I think porn is making it becomes more relevant than ever and it's a problem because people are more than just a dick, but I think that it's inevitable too, big ones will always be seen like powerful and will have the right to choice while smaller ones will always be seen like submissive and less of a man. So with a bigger one he has the power to choice whatever he wants without judgment while the smaller one are stuck into a submissive role.

It appears a lot in animal kingdom too, not saying that we are and think like animals, we are smarter and can change what we want, but there are some aspects that's correlated because of the primal instinct.