Because things happen. There will always be bugs.
I’ve played plenty of games, smaller and bigger than WoW and these kind of simple things just don’t happen this frequently.
It is a result of no one seemingly taking ownership and seemingly no one being reprimanded for mistakes.
24 hours later and its still not fixed. EVEN THOUGH THEY DID A HOT FIX THIS MORNING. 
According to WoWHead, the in game tooltip is wrong. It is in fact for TWW dungeons even though the tooltip says Dragonflight.
Was reading an article about it this morning, I’ll see if I can copy link from guild discord and paste here.
I hope that posts an actual link, but I imagine copy and paste to browser will get you there as well