Did the OP ask for and receive a replacement set of headphones? Any large-scale operation requires methods for correction. Twice I've had to request replacement headphones on Polaris flights due to broken connectors, but they aren't a problem to procure from the cabin crew. Personally, I prefer using them, and find them more than adequate despite not being the very best one can purchase, as it saves me from carrying a bit of kit around that will undoubtedly get lost.

If the OP didn't take a basic action like requesting a new pair, then why complain here, rather than to UA customer service?