If you date someone for 2+ years, at that point, you know what their opinions are on all meaningful topics. All there is left to discuss is small talk: how's your day, did you like the TV show, etc.

Unless your both happy sitting in silence, you'll probably drift apart.

Edit: I think the issue a lot of people here have is not small talk itself, its small talk with strangers. Asking a loved one about their day is small talk, but that doesn't diminish its value.