People's lives are just different now. Instead of everyone coming home, eating dinner, and then sitting in front of the TV all night watching one channel or another, there are far more time sinks out there. People use their PCs, tablets, smart phones, etc to access various parts of the internet for gaming, socializing, music, and even video entertainment.
The latest changes have shown that for years many people were watching prime time TV not because they wanted to but because it was that, read a book, listen to music, or go out. If they weren't too big into any of those others, or only did one, what else was there? You sat and watched whatever was decent.
Myself, I watched a TON of TV until my later high school years. At that time my socializing picked up pace, and I cut my TV to watching only the shows I really liked instead of 1-3 hrs EVERY night of the shows I thought "ok." College came and I got my own PC on top of the other things, so that cut in.
DVRs actually allowed me to pick it back up again a bit, but I only watch about 50% of my shows during the time they actually air. With 2 little ones in the house, it's pretty much a necessity if they're still awake as there is LOTS of pausing, or rewinding because they were too loud to hear what was said! We usually start watching around the time they're almost ready for bed, like 830-930, so we start when shows are already half done or even finished an hour or so back.
The Jedi Master
The anteater is wearing the bagel because he's a reindeer princess. -- my 4 yr old daughter