For one, we know everything with mass interacts gravitationally. No reason to think Jupiter is any different. Furthermore, Jupiter's gravity is evident. It has moon and rings orbiting it. We've even put probes in orbit of it and almost every probe that's been sent to outer solar system has used Jupiter as a gravity assist. We know for a fact that Jupiter has a gravitational field, no belief required.
Gods on the other hand aren't evident at all. Nor is it logical to think that an omnipotent being has always existed. How could that possible work? It creates more questions than it answers and it's not based on any logical deductions, inference from data or evidence. It's a far fetched hypothesis.