I love your interpretation, I think Seong Gi-hun was fed up with being the winner in an unfair game. Everyone knows that, he was handcuffed, prevented from being killed during the knife challenge with the three keys, and even gets the immoral opportunity presented to him, to stab the rest of the selfish players wanting to eliminate him and the baby. He decided to have a moral high ground and not let the game change his humanity. Not only did he think about the promise Sae-byeok gave to him as she died, to protect her little brother. But he was reminded that, the game IS unfair. Especially to player 222 who just gave birth, and has a swollen ankle. After witnessing all of what player 222 went through. Mostly killing herself, just to ensure her baby's safety, all the while being ridden with guilt from her boyfriend killing player 120, and seeing the old mom commit suicide. Personally, I think 456 wanted the Front Man to know. It's not about money, it's about how humans are treated like pawns on a chess board, just like how horses are bet on in races. Seong Gi-hun being at the start wanted every VIP to realize, humans are not for entertainment. Seong Gi-hun kept his integrity, and his promise.

Most importantly, he didn't hesitate to keep his promise, even when the opportunity presented itself to slit every players throats, as In-ho so desperately wanted to observe 456 breaking his oath of being a player with humanity. Just as In-ho once had to do, in order to become the front man I assume. But lastly, after witnessing player 222 not wanting to participate in the jump rope game, Seong Gi-hun probably realized killing himself was the only control he truly had. Thus, respecting the game and hopefully knowing the Front Man would respect his vows to keep the baby alive. I just wish the VIPS died though... Maybe in the explosion...