Attendance is down pretty much in all sports.
Tech for sure IMO is a cause, we saw this coming miles away.
Who wouldn't pick the comfort of their own home with your AC, big screen 4K high def TV, surround sound, refrigerator, and private bathroom. (OK, I personally don't have a big screen TV, surround sound, but some people have nice set ups or man caves)
Maybe attention spans have decreased as well?
When the camera pans the crowd everybody is on their cell phones. Personally I feel tech has killed my attention span. (I have to walk now while reading a book to stay focused, because my mind wonders in all directions.)
In pro sports IMO it's increasing ticket prices, concessions, parking, and even politics. When I think of the cost to go to a game with my family of four I just quickly talk myself out of it.