Binge watching and on-demand viewing aside, there's also just a lot more fragmentation of TV viewing. Even a hit streaming show like Game of Thrones has much lower viewership than hit network shows did at least in the US.

But certainly the asynchronous watching has an effect too. "Everyone" watched Seinfeld etc. on Thursday night. Today, even for shows that drop weekly, most people are just out of the habit of watching shows as soon as they come out.