I don't know why people keep saying this.
Gon didn't become a Hunter to meet his dad. He became a Hunter because it sounded like the most amazing thing, and catching his dad was just a way for him to prove he'd reached a certain level of skill at Hunting.
Now that he's no longer chasing his dad, he's free to hunt what HE wants.
It's also a shounen series. Shounen series don't end until their main characters are the most powerful characters in the series. And even though Gon met his dad, he's clearly not stronger than him. I mean, shit, even Ging is only a 2-star Hunter, and there are apparently 3-stars. Gon doesn't have any stars yet. And the series just introduced an entire new dimension of potentially stronger characters out there.