I have a relative who was one of the last venue managers of the old SFS. He said it was a death trap in terms of emergency access and egress, and they had been told by the emergency services that after the existing safety certificate it would not be extended.
Now he retired before the decision was made to knock it down and rebuild it, so I have no idea how much it would have cost to fix that, but I imagine it couldn't have been cheap. In addition to re-locating the corporate seats to the sidelines, probably would have been fairly expensive.
My question about the SFS remains why did it have to be a 45,000 seat stadium. A 30,000 seat club stadium would have been perfect for the Roosters, Rabbitohs, Waratahs and Sydney FC. It also would have been fine for most Socceroos games and non-Bledisloe or Lions Wallabies tests. Concerts would have the ability to use the SCG and Accor if they needed the larger capacity, but there are a number of 30,000 seat stadiums that are designed with a modular end area for a stage that allow them to hold 40-50,000 for concerts.
Once they decided they weren't building a 65,000 seat stadium at Moore Park and sell off Homebush and demolish it like Baird wanted to do, I don't know why the SFS wasn't designed as something more boutique, but with the flexibility to hold more for concerts.