Is it because They are friendly and non-aggressive in a Buddhist sort of way? No! Generally speaking, every deity is capable of exercising violence if provoked and several preside one way or another over military conflict, be it defensive, aggressive, or both. The Gods are not “gandhis” (most of Them, anyway) and They are not all equally sociable, which means some are more willing to watch over humans than others.
Is it because the Gods preside over the kind and nurturing elements of life? Again, no! Apart from the already mentioned deities that deal with the affairs of war, some divine beings are responsible for unpleasant things such as disease, vengeance, and death. And this is true not just for the Gods of the underworld, which are obvious, for also for deities usually seen through much more pleasant lens: to name three examples, the shinning and healing Apollo has a hand on plagues, the golden and life giving Ingvi-Freyr has a darker side as God of the Mound, and the vigorous as well as invigorating Dionysos can also inflict madness or a deadly frenzy. Gods are often two-sided like a coin, presiding over related good and bad things.
Is it because They are willing to forgive and well disposed to assist us? Well, some may be more than others. Different gods have different natures and not all are equally forgiving or sociable, as already pointed out. Besides, one should keep in mind that the Gods have Their own agendas and greater deities, i.e. those that preside over the greater cycles of the world, may be willing to sacrifice individual lives for the sake of Life as a whole (for more on this, see here and here).
Still, from the three listed above, this latter point is the one that comes closest to my idea of the Gods’ essential benevolence. But before that, there’s one last thing to consider, or rather two: freedom and pietas.