It's a compulsion as old as sports itself. It's more pronounced in other sports, where well-honed recruiting infrastructures will soon feature time-traveling, but it's present in MMA as well. Everyone's always looking for the next big thing.
From the UFC's perspective, the entire rest of the MMA world is a series of feeder leagues, tributaries of talent flowing down to that fathomless octagonal sea. People with a wider view know better, as Bellator, Europe's Cage Warriors, Asia-based ONE Championship and others are cultivating and showcasing their own talent all the time.
Nevertheless, the UFC has one heck of a strong cherry-picking hand, and often have the leverage to take what they want.