It has been my experience that as soon as implementation is over business carries on and other priorities come over the hill and the focus is lost. The other factor is the disconnect between the values on paper and what they mean in reality, leaders and their people are often confused as to what is expected of them and how they are meant to change. Without this being clear and continual reinforcement the momentum is lost.
The other factor is the character of the organisation leaders. If the people do not see the leaders walking the talk they soon write the values off as a sham and get on with getting on. The values have to come from a place of sincerity not as an item on their to do list that they have to do to meet their KPI's.
The key ingredients to a successful values program are: A sustainable program over years; commitment and change from the leadership team - no exceptions; the link between values and actions clearly articulated so people understand how to do the values; programs that involve your people in their creation are the most successful.