The old app was Apple's maps app, that just happened to use Google APIs. And of course, to use Google maps data without letting Google show any ads, you have to pay Google. And if you have 400M iDevices, the number you have to pay Google is probably in order of >$50-100M per year (or something like that - I have no idea; just wanted to say that it's a lot). And even after paying that much money, Apple still didn't have turn-by-turn navigation or vector maps (the rumor is that Google wanted more user data and Apple refused).
So, Apple decided that instead of giving Google $500M in the next few years, to spend that money on developing their own mapping technology and be masters of their own destiny. Sadly, the result is laughably worse than Google's data, and probably will be comparable to Google's 2011 sometime in 2014.