There are a number of reasons, and these are:
Poor scheduling of games for Thursday and Friday nights when people have to get home from work - and commuting in Sydney takes hours.
Stadiums are no longer in the local area or near the clubs. Public transport requires changes of mode, and parking is expensive, or not available
The quality of accommodation and price of entry, food and beverages is poor value for money.
There is virtually no shelter from the elements at most big stadiums, and putting a crowd of 30,000 in an 80,000 seat ground kills the atmosphere.
The length of time between lower grades and main game is too long
The quality of "entertainment" between games is appalling
The high decibel advertisements that drown out conversation is annoying and unnecessary. If we have to suffer ads, entry should be free.
The standard of play has become boring, with one out running and fifth tackle kicks the norm
The standard of refereeing has made the game look like some teams have it rigged in their favour
Winning. People will come out and support their team if it is winning most games. Nobody wants to pay good money to watch their side flogged every time.