Because 456 contestants will make it difficult for viewers to connect with participants, so they won't care who wins. And it doesn't really matter if they're playing for $456 or $4.56m.
It’s Squid Game. The whole point is that the first few rounds are bloodbaths, you’ll have your core cast after the first few episodes.
Not to mention it’s prerecorded so all your central members will get the producer’s favourite edit from episode one.