They last about 5 seconds now. Why does Blizzard break everything fun in this game?

Word on the street (Or at least the mouth-breathers on Wowhead) is that it's just a glitch. Not intentional.

But yeah. Elder's Moonstones are affected in the same way, and they're harder to come by than Stones of Elune. Now might be a good time to capitilize on stupidity and buy Elune stones while the sky is falling.

My guess is because they have serious problems with control of their code.

I doubt this was intentional. It's likely something like last patch where Power Word shield from that priest you could barely see sounded like he was Power Word Shielding your eardrum. Just some random thing that broke accidentally as a result of changing something else on purpose.