I know 5 German words now!

[Innkeeper]

Dry Auslese tastes like Dry Riesling with high alcohol. That is because it is high in sugar to begin with. The reason why it is rare is because Germans don't like high alcohol Riesling.

That is the traditional answer. Now-a-days, with all the high tech monkeying around that they do with wine (the Germans are past masters at it), you never know. Maybe they take some of the alky out of it. That would still not explain why they didn't make sweet Auslese out of it to begin with.