This is really exciting. There were a ton of questions we all had going into this, like "why bother betting after the cards are revealed and when you have already learned the law?" but now we know why. This game has so many layers to it. I have to really give the author credit here with this game. A lot of times in gamble manga, the gambles are games that seem straightforward at first, and the thrill is watching how the protagonist unravels the opponents cheating, or the odd twists and turns a game will take as the protagonist unveils their master strategy like in the two Labyrinth games or say, in Kaiji's E-Card gamble. Compare, say, Hangman, where the object was discerning how Sadakuni was cheating, to this, where there's so much to keep track of. This is a game that just gets more and more complex the more we learn about it. I'm extremely impressed at the design of this gamble.
@Naiyro
They don't know the hand the other player will be making or even the card that the other player is using. On a basic level they want to make the strongest possible hand to help their allies down below win as many hands as possible, however as we've seen there are some unwinnable matchups between the cards. We see that, in the example of 35 vs 6, the only way 35 can beat 6 is in its strongest form, the straight flush. If 35 can't form a straight flush because the cards required to do so are lacking, then it cannot beat 6 at all. Of course, 6 is only so strong because of 4 of a kind aces, if those are gone then 6 is out the window as well. Lalo's 47, for example, is completely unbeatable in its strongest form, but it has to be played while it can still be formed, and Fukurou HAS to pick the royal straight flush for it to be the unbeatable 47. We saw what happens when you blindly make the strongest hand in this round; Hal made the strongest possible hand out of the 45, not knowing that Fukurou had 47 and there was a card overlap. This caused the calamity.
The gamble they can take is to
not make the highest possible hand. Remember, they are only punished if they don't match their hand to the numbers, use a card that was used previously, or simply don't pick in the time limit. Depending on what cards they pick, they can save cards that they can use later, making some of the weaker cards stronger because they have more cards to play with, or possibly interfering with the others stronger hands. Of course, the cards they pick are known after the match, so those cards that were saved or used are known by the opponent. However, this information is NOT given to Lalo and Baku ; they don't actually know if their cards are being made into the strongest possible hands or not, or the actual cards in the deck that have been used by their partners. That's just an assumption we've all had because presumably thats the way the game has gone to this point. Additionally, Fukurou and Hal don't know the other numbers Lalo and Baku have in their hands either; they only know the ones being played at that moment.
They are encouraged to make the strongest possible hand because a single round could mean death for their partner, but they are not required to do so. And as we've seen, making every hand the strongest possible hand can backfire ; Hal and Baku experienced the calamity because they tried to make the strongest possible 45, and their cards overlapped with 47.
The mindgames are extremely complex and multilayered in this game, and we see now why Baku is (presumably) trying to communicate with Hal. Hal and Fukurou don't know the opponents cards or the other numbers their partners have. Baku and Lalo do not know the hands their partners are even picking, let alone the hands their opponents are picking. This is why resolving the law drives you deeper into madness; we thought Lalo and Baku had a ton of information to go with and that they would instantly recognize a winning or losing card, but in reality they have been betting blind. I'll use an example to illustrate this
Say, for example, Baku tries to play 25, his ace card. Hal could:
1. Pick the strongest hand and have Baku simply play straightforward and win. This is what we've been under the assumption that was happening, that all cards are required to make the strongest hand possible. Upon seeing 25, Lalo could respond by folding immediately, because he would recognize 25 as an ace card. If Lalo bets, then Baku takes him for everything.
2. Pick a lesser hand that still forms 25. Without communication, Baku would not know that his 25 is not an ace card anymore and has been devalued. If he plays it straightforward and bets on 25, and Lalo also assumes the 25 is the full value straight, Lalo could fold and Baku would win with a weaker hand. This could possibly interfere with Lalo's remaining cards (perhaps even causing a calamity if he forces a card overlap). However, if Lalo were to call it, and Fukurou made a stronger hand than Hal's janky 25, Baku could lose with his "ace card".
Both sections of the tower are, right now, still mostly playing blind. If they somehow find a way to communicate, they can tell their partners what hand they have, but not their opponents. If both sides figure out a way to do this, then the game can start to resemble traditional poker, where you could bluff and gamble. In my example, if they could communicate, Baku could tell Hal what he wants, and Hal could make the hand Baku desires. Then Baku would know what he is betting on rather than a hunch or assumption. Of course, they would still not know the hand Lalo and Fukurou are forming (other than the hint of the number it has to form, assuming they don't make a clusterfuck hand and take a loss for no reason other than to screw up some other hand).
As well, it looks like losing a hand is not without cost for the upper players; whatever happens in that iron maiden seems to really fuck them up. Hal's brain looks fried.
Layer all these hurdles the players have to overcome with the inherent time limits of oxygen and "no delaying" rules of the game, and it becomes an incredibly stressful situation and an insanely deep gamble.