http://www.worldfootball.net/attendance/ita-serie-a-2013-2014/1/
Should've said big 5, probably. Around 15,000 then. Ludicrous.
Bit of wild generalising but it's gone the way of over here in the late 70s/80s for a lot of teams. Shitty grounds, threat of violence from fans/police, low standard of player compared to what was. Football mirroring general society. Shame.
Shitty grounds is the biggest factor. Disproportionately sized, outdated and council owned. Slow and problematic bureacratic process makes it extremely difficult to get new ones. That coupled with every game being on TV means you have vast empty stands, which means you have a poorer product, which means you struggle to promote the league around the world. That leads to less revenue and poorer standard of play on the pitch.
Juventus are the only club in the 21st century, basically.