The author got bored and figured that Tower of God could be a decent manga to borrow from
quite a few death game manga have an "open world" arc e.g. battle 5 seconds after meeting, iirc alice in borderland and kamisama no iutori as well
I don't mind it since it's a good way to introduce quite a few more characters but hopefully the author remembers to keep the arbitrariness and huge spectacle of the water tower and bull games and doesn't let it turn into simply "a bunch of people with powers fighting each other "