The simple reason lawyers continue to decline in how the public views the ethical conduct of attorneys -- at least to a Gallup Poll -- has to do with self-regulation. While all attorneys may believe they are 'ethical', the problem is their only source of reference are other lawyers.  If attorney "A" wins a case being less then ethical and the judge lets the conduct slide. Then attorney "B" thinks that is a viable tactic. This beings the 'degenerative cycle' of legal ethics.  

When lawyers become judges that point of reference doesn't change just because a lawyer trades his pinstriped suit for a black robe.  This is a closed system -- they only have themselves as role models.  There is no real outside reference because lawyers consider themselves 'the law'.  Who can tell them differently -- we non-attorneys are intellectual neanderthals.

This 'degenerative cycle' can be stated by the more familiar 'boiled frog syndrome'.  What this means is if you place a frog in boiling water it will want to jump out.  But if you place the frog in warm water and slowly raise the heat it will politely boil to death.  What this means is that very slow changes in the environment goes unnoticed.  Until, what you once were is no longer what you actually are.

As lawyers take one baby-step backwards on the ethical road towards enlightenment, they establish a new, but lower, standard.  A small step backward from this new, but lower standard, establishes yet a new standard.  Very soon the legal profession has adopted such a low standard that they no longer look ethical to the rest of the population.  They don't know they are becoming unethical, they simply haven't changed their reference point ... which point keeps getting lower.