Why has the 3DS so much quality titles?

[Mnementh]

Think about it: DS was a miracle that sold 150+M units. The 3DS while not bad is currently only at 50M and will struggle to reach 80M. Still it has the much better library. Use Metacritic as comparison:

http://www.metacritic.com/browse/games/release-date/available/ds/metascore?view=detailed

http://www.metacritic.com/browse/games/release-date/available/3ds/metascore?view=detailed

Metascore of 90+: 7xDS, 7x3DS

That is the case, although the 3DS still has 2 years of life left. And a lot of games still are coming: Bravely Second, Youkai Watch, most likely another Pokemon.

So despite the smaller install-base the 3DS gets more quality games. Why is that? Discuss!