The National Spelling Bee contest has been going on since 1925. I went and looked at how the difficulty of the winning words has changed over the years. These are the last words that the winner has to get correct in order to clinch the championship, after all the other contestants have struck out.
In the first ten years of the competition, the winning words were: gladiolus, cerise, luxuriance, albumen, asceticism, fracas, foulard, knack, torsion, and deteriorating. Of these, only cerise and foulard were unfamiliar to me but I think I could have guessed the spelling correctly. These are words that one encounters in everyday use.
Now take a look at the winning words from the last ten years: appoggiatura, Ursprache, serrefine, guerdon, Laodicean, stromuhr, cymotrichous, guetapens, knaidel, stichomythia and feuilleton. I have never heard of these words before, have no idea what they mean, and my chances of guessing right for any of them would be very low. One is unlikely to ever hear them used except in highly specialized contexts.
So clearly the standards have changed. In any competitive event, one expects the standards to rise as people learn from the past and get better at doing whatever the contest requires. This is inevitable and in general a good thing. The problem the spelling bee faces is that the only way to raise the bar is to make the words more and more esoteric and thus become less and less relevant. Without changing the format of the test so that more ordinary words become relevant again, I think it is doomed to become even worse in the future, if you can imagine it.
I think there are ways to do that. One way would be to have all the students get the same set of more ordinary words and write down the spelling with only a limited time to do it. This not only would be fairer, it would give an advantage to those who read widely and would recall the spellings immediately because they knew them, rather than trying to recall what they had memorized.
But it seems like part of the appeal of this contest for spectators is the cruelty of watching a gladiatorial contest in which young students sweat and then flame out so things are unlikely to change as long as it is televised.