If you think about it, it makes strategic sense that, if Apple were going to break out on its own for mapping data, they would do so while there was significant time remaining on the maps license with Google. iOS is on a more or less annual development schedule. iOS 6 just arrived last week. iOS 7 is probably not coming until a year from now, and even if it’s on a more aggressive schedule, Apple would surely seek the luxury of having the option to wait until a year from now to ship it.
An all-new maps back-end is the sort of feature that Apple would only want to ship in a major new OS release. Technically, they could roll such a thing out in a 6.1 or 6.2 update, but major changes — and I think everybody can agree this has been a major change, for users and app developers alike — should be delivered only in major new OS updates.
But if the old agreement between Apple and Google expired in the first half of 2013 (which, again, my own sources familiar with the matter agree to be the case), that means the deal was set to expire halfway through the expected year-long life cycle for iOS 6. If Apple had stuck with Google Maps for another year they would have been forced to renegotiate with Google in a situation where both sides at the table would know that Apple either (a) had to agree to whatever terms Google demanded to extend the deal; or (b) would be forced to swap the mapping back-end of iOS 6 midway through its development cycle.1 However tumultuous a change this has been in iOS 6.0, it would have proven more tumultuous and controversial if Apple had been forced by failed contract negotiations to squeeze it into a 6.1 or 6.2 update come May. And, that would have forced Apple to devote significant engineering resources for an iOS 6 update that could otherwise have been applied to iOS 7. Big changes come in the major release; bug fixes, security updates, and minor improvements come in post-major-release .x updates.
Whatever chance there was for Apple and Google to agree to a longer-term deal for iOS to continue using Google Maps, the effective deadline for Apple to make that decision was earlier this year, not next year when the existing deal expired. Apple wasn’t going to wait to negotiate until their backs were to the wall with the currently-shipping version of iOS reliant on Google Maps when the old deal expired.