Apparently Yin Tianzheng had matters come up so he couldn't attend, but what in the world could possibly be more important than the Dragon Sabre? The whole wulin coveted it, and it was a bunch of nobodies that showed up to view the sword.
What was the point of showing off the Dragon Sabre to a bunch of nobodies instead of immediately sending it back to the sect and trying to figure out the secret?
Considering how the whole wulin, including the super powerhouse sects, reacted to the sabre later on in the story, it's obvious how important it was.
This just seems like a giant plot hole that is overlooked and I don't think has ever been discussed.