@boomerang,
I loooove
Forest Gump. One of the better movies of the past 30 years or so. (Parenthetically, I've liked just about everything Tom Hanks has been in. Maybe it's him or maybe he just gets good roles.)
I enjoyed
Da Vinci Code, but that doesn't mean I'd label it as art or good literature. (I have explained elsewhere, on at least two other threads, why I enjoyed the book and why I think it's hilarius. The Tom Hanks movie, in this case, didn't cut it. It doesn't take full measure of the nuttiness of the book.)
But, to answer your central question, certain things get labeled lowbrow because, well, because they're so
lowbrow. Your next sentence comes up with an interesting observation. You say:
Seriously, there are thousands of worse movies, books and TV shows but these three seem to have some kind of pop culture signifigance in that you're only "okay" if you hate them.
The point, I think, is that these have become popular pop icons. It's okay to be terribly "lowbrow" as long as you, as an artist, don't start to claim an abnormally large portion of the public's attention. Nobody really cares or makes a fuss if you like Harlquin romances. Why? They're not on any best-seller lists. Dan Browns execrably wretched imitations of prose art are.
(Still don't know why
Forest Gump would be on that list, though. Great movie.)