I think all states should have primaries. And, I think if Washington Republicans can have a primary for delegates, Democrats should certainly do so as well. I would hope this is something the party can work on for the future once we have our nominee.
The Washington presidential preference primary was created by initiative. As such the politicians hate it. This is particularly true in Washington since the regular primary is designed to curb the power of political bosses. The voters don't necessarily like it because they have to disclose party affiliation for the presidential primary/
When the initiative was passed in 1988, Washington was still voting in person, and voters could go to the polling place and ask for a Democratic or Republican ballot (the regular primary was and is in late summer, and does not require public disclosure of affiliation).
Since then Washington has switched to vote-by-mail. Voters have to sign an affiliation that goes on the outside of their ballot envelope. If it is filled out, the voter is reported to their party, and the ballot is counted.
In 2004 and 2012, the primary was cancelled, but only on a temporary basis. Generally it was portrayed as a cost-saving measure, but it was also likely political. The 2012 primary was canceled by Democrats, who had no need for a primary, and didn't want to risk giving any boost to a Republican challenger.
The Democrats have generally not used the results of the primary to allocate delegates (and in general the states have no control over internal party matters such as choosing delegates to a national convention).
Last year, the odd couple of SOS Kim Wyman and Senator Pam Roach proposed switching to a March primary. As part of the deal, the parties would have to elect at least one delegate based on the primary results. If they didn't, then the primary would be a pure beauty contest with no party affiliation required. Voters don't like the public affiliation requirement, and they like it even worse when the Democrats ignore the results, but accept the voter list.
The bill passed the Republican-controlled senate, but never got out of the House committee. There was speculation about cancelling the 2016 primary, but apparently there were not Republican votes to do that. When the house committee heard the bill, some Democratic central committee members testified against it (based on appearances they were either longshorewomen or teachers union.)
The current primary statute calls for the May primary, but has a provision that the date can be changed by a committee comprised of the SOS, the chair and vice chair of the (two) major parties, and the majority and minority leader of the two legislative chambers (so 4 Republicans, 4 Democrats, and the SOS), a change requires a 2/3 vote.
So SOS Wyman chirpily had everyone introduce themselves, and explained the advantages of an earlier primary, and then a motion was made to change the primary to March. It failed to be approved on a 5-4 vote.
As part of an effort to score points against the Democrats, the Republicans are choosing their delegates based on the May primary (in the past they have used a mix of caucuses and primary votes).