KasiCair
At this point he's just doing it for his own amusement. No one in the WW poses a real threat to him and combined with his meta knowledge, money and magical power he could wipe them out easily. Only Dumbledore could pose a slight threat to him due to the death stick, phoenix and stuff introduced in fantastic beasts. However once again this won't be the case for Hermione and especially Harry who she would follow anywhere. While the Voldemort problem could be solved easily, Dumbledore is a real threat to Hermiones safety and as long as Tom plays with his prey then Hermione could either die or be used as a bargaining chip against him. His time in the WW feels more like a Holiday where he makes fun of the natives constantly for his own entertainment. If he truly cared for her well being then he would have solved those issues already. Besides there are multiple end of the world scenarios he should concentrate on with his meta knowledge. Thanos, Apocalypse, the phoenix force, Galactus, Ophis - just to name a few. Sure he still has time but can he really waste his time in the WW without at least trying to gain something there? So far he doesn't seem to care about anything there. Once again: time turners, liquid luck, the mirrors and other enchanted relics/objects could be a game changer for him.