Once again the idea that players are all on the same contract and all have equal value to other clubs. Garner and Eisenhuth will be on minimum salary or close to it, so there is literally zero value in releasing them unless they need the roster spot: they don't free up any cap room at all, as they have to be replaced by someone else on at least first grade minimum. If Penrith need to free up cap space they have to release someone who is making some actual money, not just a warm body. Personally I'd be surprised if they decided To'o was the most expendable but who else is on that roster, making decent coin and not vital to them? Yeo? Edwards? Cleary?
This is the same argument as "why did we let Papali'i go and not Bateman?" It's because another club is willing to pay Papali'i's contract as he is still perceived to have some value, whereas barring a miracle the only way anyone is even going to consider taking Bateman off our hands is if the Tigers pay almost all the money owing to him.
EDIT: besides, what Penrith have shown they do really, really well is working out which of their players they absolutely have to keep even on big contracts and which they can live without, replace with kids etc. They've let the likes of Kikau, Koroisau and Burton go without dropping a beat, and there's every chance losing Crichton and Leniu go isn't going to stop them, either. Eventually their run has to end and one would have to think Luai and Fisher-Harris leaving would be as big a challenge as they've faced, but still: sensible roster management doesn't mean never letting a good player walk. In fact, in some cases it means the opposite: not being emotionally attached to players to the extent that you prioritise keeping them over what they cost you.