Why did it take humans so long to invent gravity?

You're right, it's hard to believe it wasn't invented earlier. And that's because it actually was; several thousand inventors, including Kepler, Aristotle and the Pilgrims, created a variety of gravities long before 1673 but the huge tentacles of the international rope and anchor conglomerates kept finding the inventors and buying and then suppressing their patents to prevent loss of business. Finally Newton had the integrity (and the integrals) to stand up to them and refuse their offers. And showing admirable foresight and generosity, he put the patent in the public domain, so no more buyouts are possible. Of course we're better off now, especially since Newton's invention is a universally applicable version and absolutely free, but sometimes I miss the angels with their beautiful gossamer tethers...