To make a long story short, it is reasoned out by the "Judge" that Baku's treatment up to that point was based on prior events and decisions, but that it is necessary to carry out the collection as soon as the current game is over and the ban on violence is lifted to finally tie up this loose end and prevent a similar situation from happening in the future (Chapters 97 & 100). In other words, if Baku had lost and the date had returned to him, Baku would have been the one to be killed at the end of the game.
To make a long story long, based on what has been revealed in the story up to this point, Baku had special treatment solely because he was the only person whose life had ever been spared by Leader in that way.
Normally, even in this case he wouldn't be allowed to:
- Use Kakerou after the collection deadline, or
- Gamble with his life, even prior to the collection deadline,
But since there was no defined deadline for the collection of Baku's life, and Yakou had already allowed Baku to take part in the abandoned building gamble (the vague terms of which, notably, did not indicate that Baku was betting his life), that precedent decision also carried forward into the deserted tunnel gamble. It should also be noted that the reason Baku's life wasn't collected after the deserted tunnel gamble was that he had Kyara acting as his insurance, although Baku provides the pretext of forgiving Leader's failure to pay his personal bet in exchange for being allowed to walk free that time (Ch.67). With all that said, the Judge makes the final decision to "put [the] matter to an end today" and enforce the collection with the end of the labyrinth gamble after receiving Leader's implicit permission to "throw away" the past (Ch.100).
Now, outside of the story, the decision to collect is a necessary move by the author to maintain not only a sense of stakes for the final round of the labyrinth gamble (i.e. Baku won't just get off scot-free and go back to the status quo if he loses), but also a sense of stakes for the overall story, since leaving Baku's life constantly up in the air never to be collected would get tiring and eventually run the risk of making Baku seem arbitrarily invincible against Leader.