The same reason lots of other things aren't resolved on it.
(Like 3 USIMs working, Nokia native FM receiver, and portrait mode browsing, for example).

Because if they waited until their Ovi department had everything ready, we'd be complaining even louder at how long it's taking to ship the devices!

Never underestimate just how long it takes to sort out something like Maemo-friendly Ovi, with all it's commercial and legal aspects, and massive cultural differences (i.e. inertia) from non-Maemo-friendly Ovi. Probably most of the people working on Ovi (by which I mean non-techies, mainly), still don't have a clue about open source, and there's just a few people trying to spread the point.

Apple made it look like setting up an app store was easy, but they were planning it for years in advance. You just didn't see it happen out in the open.

Whereas the N900, Maemo 5 open source thing gives a great impression of being rather a surprise to Nokia as a whole.