Google was using their Maps as a weapon against Apple in the Mobile Wars. Apple, not wanting to be dependent on a hostile competitor for a major service, with their customers clamoring for feature parity, did the only thing they could do. They're screwed either way since mapping takes time to get right, due to the complexities of incompatible reference points for local data, transforming a 3D mostly-spherical object onto a 2D plane, inaccuracies created by out-of-date and imprecise measurements done at different times with different tools and methods, and of course the imprecise nature of floating points in the digital environment. The world is a very big place, and mapping it on a computer isn't easy.
Faced with the choice between getting screwed over by Google for another year, or putting their customers through an error reporting process they'd need to do anyway to get more accurate map data, Apple made the logical decision to release Apple Maps sooner rather than later. It gets the necessary growing pains over with sooner.
Maybe you don't remember how bad Google's maps were in the beginning, or people just gave them more slack since it was a minor, experimental part of their business at the time (they used to be a web search company).
