If we shared all content exactly equally what we were interested in, it would point to incredible levels shallowness in nearly everyone- the innate assumption that everyone agrees with our views.
Fortunately, there are enough people who DON'T assume that to distort the agreement in the two traces in the second plot. (There would be a few who would make some moral or philosophical commitment to share only what truly interested them, I suppose, with intent to broadly educate.)

Also, guys would have long ago made sure that porn overwhelmed the entire Internet, not just most of it.