I'm aware of the history of the show and how a TV show is financed. And it's not the first Big Brother franchise that got passed around like a hot potato. None of them treated their fourth or fifth reboot as a trial run. They might have had less budget but they had it because of budget cuts across the board.
Reviving BB was a risk that Ten needed to mitigate, especially with a three-year commitment.
With a three-year commitment, I'd rather believe that they might have thrown more money at it than they would have done for any other show. Because it is in their interest that the audience comes back in the second and third year. I would compare it to a business like OpenAI.. but not like this:
This show is a business, and businesses need to be proven as viable before backers go all-in on investment
OpenAI hasn't proven that their business is viable long-term and backers go all-in on their investment all the times. They invest the money because they believe in the business and will make their investment back later. The only thing they can go by right now is interest. (As a side note/question.. I've cited the first seasons of shows that haven't existed in Australia before and thus couldn't proof if they are viable either. Why are they not falling under your definition of trial/pilot? If they would, it'd be easier for me to understand your point.)
As for the interest in 10's first new series. I don't think they were worried that audience wouldn't come back for the first one. We have enough evidence that the Big Brother audience comes back. They came back after 10 screwed up their final year. They came back after 9 screwed up their final year. Why wouldn't they come back after 7 screwed up their final year. They only leave once it turns bad.
And I wouldn't believe that 10 will be throwing more money at it next year just because of the love for their show. If anything, they will throw more money at the things were money is needed. But everywhere were cutting costs worked out for them, they won't provide more money. Why would they? It's a business, business wants to make money.
Also, if anything, I'd consider next years season a trial run aka the one that needs to proof that the show is viable. Since 2007, Big Brother has always lost at least 17% of the audience that they've had in the previous year. The only time the show gained an audience was when there was no previous year, e.g when it came back from a hiatus. And with TV and streaming ad revenue expected to decline even further in 2026, I would be a lot less optimistic that 10 will throw with money left and right.
They will spend more money on the things where money is absolutely needed and keep the rest for themselves, e.g. if they finally decide to hate having Tailspin riders talking to the house, the house will be somewhere else. Otherwise, the house will be exactly where it is right now and they won't spend an extra dime on building their own shed for no extra benefit.