I don't think it's about money at all. It's a brand new, shiny multipurpose stadium that they want to look good and not have to compromise the nature of the venue by dragging over the old cheap crap from the shanty town arena.
No one wants to go to an Adele concert in 2020 and sit in the Old Bastard Who Played Sport in the 1970's Pavilion. Yes, I realise I could have ended that sentence much earlier.
If you go to a Fremantle game and they can do the place up with the history of Fremantle, and do it well and update it as needs arise, and then the next week switch it around and do it for the Eagles, and then in the summer make it the home of cricket and alter it for whatever else they hold there, then you'll get a much better stadium than you would if you had to dig up the world class, professionally landscaped exterior of the stadium to put in some cheap pavers highlighting that Gus Seebeck won a medal in a local football league that would never be able to fill the stadium you're about to enter.
Now, I'm obviously imagining holograms and laser shows whilst he's thinking of putting the name Pavlich on a digital sign but I think the point stands.