@thed - I am guessing it's because they don't want to give it away for free. I don't know why they don't just make it a paid app. Here on IOS is trash, it's not the same as Nokia Drive, just a token app wrapper around their website.
@subkamran - Navigon is probably a good choice. Garmin and Navigon use Navteq (Nokia) maps, so it's probably a similar experience, maybe better in some ways. The challenge is that it's not free. Honestly, I'd rather buy a GPS unit than pay $40 for an app. I understand how you want Nokia Drive for free, but giving it away for free is not in the cards as far as I can see.
Just in case I wasn't clear. The 'Here' app for IOS is not the same, not even close. It doesn't have voice guided turn by turn ... it's just a C++ wrapper around their website so they can call it an app. OK, it's a bit better than the website, but not much. Nokia Drive is still exclusive to Lumia and will likely stay that way until they can get a good deal for it.
And just in case you are wondering .. Hey ... Microsoft is paying all that money to Nokia ... well .. as I've covered before, Nokia has also committed to buy far more Windows phone licenses than they can sell phones, so it's actually evening out ... for now.