Hubert Farnsworth cloned himself a clone to finish his accomplishments and to become his legacy after he passes away. That resulted in the creation of Cubert. The purpose of Cubert was to finish the inventions of Hubert Farnsworth.
However, the show, has there been any indication that Cubert finished any of Professor Farnsworth's inventions? If not, wouldn't that make Cubert a failed project, since he doesn't do what he was cloned for?
The show did indicate that Cubert called himself a failed experiment, but that was before Cubert decided to become a scientist like the Professor.