You drastically overestimate the turnover these parks have in Australia and the capital they have to spend with a view for actually seeing a return.
They might be owned by an investment capital firm with big pockets, but no park in Australia is big enough to see 15-20 million dollar capex every year. Its 100% why you see targeted, staggered spending, especially when you own more than one property.
The other side of it is, you are still seeing effects of new ride installations even years after their opening. Nobody wants to spend money until the figures start to show they HAVE to.
To be honest, i wish village would put money back into their park presentation and the visuals and themeing of their existing rides, even start thinking about their guest comfort in the blazing hot sun before they start investing in another ride let alone a whole new themed precinct.
In short. You know what makes guests happier? Air conditioning.
Bonus points if you even attempt to provide them with something to keep them amused while they are standing in queue lines.