Bronx, They still distribute it because they believe that FMV is "ubiquitous" and that most, if not all trees around the world are already infected. They also believe that it is not a serious problem.
The most attention is paid by the USDA, State Ag and County Ag, to diseases which are detrimental and injurious to crop plants. If it kills or adversely affects plants used for food (wheat, oranges, grapes, etc) and which are major agricultural products of country, then it is serious. And so on.
FMV is just not that big of an issue.