The Washington state legislature adjourned Friday evening, April 24. SB 5978, which had passed the Senate, did not pass the House. Therefore, the law providing for a mid-May presidential primary remains on the books, but it will probably not be held. In 2012 the Washington primary was cancelled for budgetary reasons, and because the two major parties preferred to use caucuses instead.
Washington state Democrats have already said they will use caucuses in 2016. The legislature comes back into special session on April 29 so it is possible the presidential primary will be brought up then.
SB 5978 would have provided for a March 8 presidential primary.
http://www.fec.gov/press/resources/2016presidential_form2dt.shtml
I don’t think it is accurate that to say that both parties prefer caucuses. The last two primaries that were held, in 2000 and 2008, the Republicans allocated some of their delegates on the basis of the primary (1/3 in 2000; 1/2 in 2008). The Democrats ignored the primary, other than accepting the list of Democratic voters.
The primary was created by the initiative in 1988. At that time most votes were cast in person, and it was practical to have voters request a ballot of a party. Switching to a mail ballot made this more complex. Voters would have to either request a ballot in advance, or somehow publicly indicate their allegiance with their returned ballot.
Democratic party activists are to the left of Democratic voters, and it chafes them that candidates for other offices can bypass them and directly appeal to the voters whether under the blanket primary or Top 2.
The last two primaries were in February, and the Democrats were able to use that as an excuse not to use the primary.