Well duh. Sonia has always been terrible and been complained about non-stop - plus she's also contracted to Seven.
As for Gretel, she's always been distancing herself from the format since she left in 2007 (there was a story where Estelle ran into her once and got a photo with her and Gretel made her promise that if it was posted on social media, there could be zero references to BB in the post). The only time she's ever really spoken about it was when it just so happened that when she was doing press after The Masked Singer AU was airing in 2019 and Seven's revival was announced at the same time and so she ended up being somewhat forced into talking about BB publicly for the first time in years. The lack of consideration for 2025 would've absolutely been mutual.