The same reasons why Apple wouldn't package Google Maps with iOS are the same reasons Google wouldn't package iTunes with Android. You don't want to concede ground to your competition. Now if they want to fight for it that is a entirely different story.
I would not however expect a company to do something that would harm them just to please me. They are a business trying to make money to survive. Doesn't matter if it is a massive company or small startup.
EDIT: Ideally I would have like the Google app to have come out a lot quicker than it did so the transition period was better but I'm not sure who to blame for that. Odds are it was Apple who pulled the rug out from beneath Google's feet during the negotiation but that is all here-say and conjecture. Probably 10 years from now we'll read in some book how shit went down.
I've converted dozens of people over to Apple and no one has complained that they should have gone to Android or stayed with Windows.
Apple would never make iTunes for Android though, so it's an unfair comparison. I have every reason to believe that Google would be willing to have its Maps application be the default.
I don't think any actual users realized that Google did not write the code for the previous Maps application, it makes no difference who writes the code. It was Google Maps, that's all that mattered. Apple already has exclusive rights to approve all iOS applications, so having a third party write the code would not be any more of a risk than shipping an internal app everyone knows is powered by Google.
To my knowledge pure Google Android doesn't package any third-party apps that tap into third-party services which compete with Google. I'm happy that they don't block any apps from being added to the marketplace and for the most part I am happy with Apple for that same stance as well.
I have Chrome, Gmail and Google Maps alongside Safari, Mail and Maps now. Heck even Google Voice competes with Siri. This is only making my life as a iOS user better.
"Pure" Google Android doesn't package anything, to get the Google applications you need to make a deal with Google. If you were able to convince Apple to make an iTunes Android app you could certainly ship it by default on a phone. Real life example: some devices from AT&T ship with "AT&T Navigation" which competes with Google's kit.
Even better would be if Apple ported its maps app to Android and offered it to anyone who wants to ship it by default. I predict a grand total of 0 devices from a large brand would ship with it.