Because contemporary ethical systems are bad. The two leading ethical systems are utilitarianism and deontology. Utilitarianism is really just a modern form of hedonism, i.e., an ethical system that takes pleasure and the avoidance of pain as its ground for "the good." Quite sophisticated versions of this philosophy have been known for millennia -- Socrates tries out a version towards the end of the Protagoras. It doesn't work because "to be good" doesn't align with "to cause pleasure and not pain."
This is true even if, as Socrates attempts, you suggest a model in which we're talking about 'the most' pleasure, so that minor pleasures now that cause worse pains later are not considered good. Sacrificing your life for your children may not bring any pleasure and only pain, but it might still be the ethical choice. Utilitarians try to avoid this problem by shifting to a kind of aggregate pleasure/pain as experienced by the whole society, but it still doesn't get it right. It still can't say just why it is more obvious for a parent to sacrifice his or her life for their own particular child, but extraordinarily excellent for a stranger to lay down his life to save the child. At worst, the movement to aggregate pleasure as the standard for utilitarianism can end up saying that we ought to sacrifice the child, especially if the death of the child can mean increased aggregate pleasure for the community -- witness the Planned Parenthood atrocities currently under discussion.
So, naturally ethicists who are utilitarians won't be especially excellent people. It's not just (as the article alleges) that they don't follow their own rules. It's that their system is pointed to the wrong ends.
Deontology attempts to establish duties. It's healthier than utilitarianism, but it still has the problem of rooting its ultimate standard for goodness. Does your duty come from reason? Kant makes an argument that it can't come from anywhere else: it is only reason that allows us to make choices that are more than actions from animal instinct. Reason must therefore be the standard for ethics. If ethics comes from reason, well, rationality is the same for all of us. Thus, we will all naturally agree about what is right and wrong. Kant thought this was so obvious that there really could only be one moral philosophy.
Empirical evidence demonstrates conclusively that Kant was not right about that. The problem, I think, is this:
1) Reason applies most perfectly to logical/mathematical objects;
2) Logical objects are like physical objects only by analogy;
3) Analogies always break at some point.
Thus, it turns out that rather than discovering laws of reason that ought to govern all human situations, we end up discovering that no two situations are really alike. We reason by analogy to previous situations, and to general working rules-of-thumb, but we can't come up with rational laws for human behavior of the sort the early moderns hoped to find. Ethicists who do state that they've found such laws and try to apply them end up doing injustice by trying to force square pegs into round holes (because the hole looks at least a little bit like a square, and certainly more like a square than a triangle).
So of course ethicists are bad people. They have devoted their lives to trying to make the world comply with bad systems. Naturally, at some point, the frustration leads them to tend to give up hope and just do what they want.