I am not a ref, nor a fan of any of them, but incompetence might be going a bit too far.
Yes it's their job to get it right... but it's certainly a tough job, happens at full speed in real time and a thankless job regardless of their call.
We have all watched enough slow-mo, HD and now SUPER SLOW 4K replays to yell and scream at that "Awful call!!!"
Sometimes, in real time... they just miss them or get them wrong. Sometimes it might be incompetence. Sometimes a grudge or make up call. Either way, it's just the human factor.
Until we have robots doing it no one will be 100% happy about the officiating... and even then I guarantee there will be issues.
That being said, it always seems to happen FOR THE PENS