Well, most of our words are words from foreign languages after all. Some are used frequently; some infrequently; some almost never. It's the nature of a spelling bee that they're going to go after the obscure words. One can also argue that spelling bees don't really test anything particularly useful (at least, for the extremely difficult and obscure words at championship level) - but as long as some people are enjoying the competition and paying attention to it, they can do whatever they need to in order to make it suitably challenging.
I wonder if they really exhausted all the obscure difficult words in the language... or if they merely exhausted all the words they had prepared in their lists. Maybe next year they will just dig deeper, unearthing words not seen in centuries. Though in that case, the difficulty is getting an authoritative spelling. But I think we can still find source material to draw from...
Whan that Aprille with his shoures soote,
The droghte of March hath perced to the roote,
And bathed every veyne in swich licóur
Of which vertú engendred is the flour;
Whan Zephirus eek with his swete breeth
Inspired hath in every holt and heeth
The tendre croppes, and the yonge sonne
Hath in the Ram his halfe cours y-ronne,
And smale foweles maken melodye,
That slepen al the nyght with open ye,
So priketh hem Natúre in hir corages,
Thanne longen folk to goon on pilgrimages,
And palmeres for to seken straunge strondes,
To ferne halwes, kowthe in sondry londes;
And specially, from every shires ende
Of Engelond, to Caunterbury they wende,
The hooly blisful martir for to seke,
That hem hath holpen whan that they were seeke.