Ye Mo had large amounts of experience catching corner soul weed and void flying snow. He knew that something as lively as this would be extremely hard to catch if he was chasing this behind. A few immortal emperors all couldn't catch up to it.
The Wu Chen fruit might not be as fast as the void flying snow but it was more lively than void flying snow. It had a sliver of space attribute too. Sometimes, you were clearly just about to catch Wu Chen fruit but it would suddenly speed up or jump through space and disappear.
If it wasn't immortal emperor chasing the Wu Chen fruit, it would be long gone. These immortal emperor could catch the weak ripples in space and thus didn't lose track of it.
Seeing the Wu Chen fruit fly towards him, Ye Mo immediately stealthed his chi and didn't even use spirit sense net. If spirit sense domain or net could catch it, the fruit would've been long caught.