Low turnout in Delaware primaries is not uncommon. Delaware In Fact shows that since 2000, the highest percentage of party turnout was for the 2008 Democratic Primary. That brought out 28 percent of registered Democratic voters to choose, among other offices, the Democratic nominee for governor (Jack Markell vs. John Carney). The lowest voter turnout came in 2006 when only 7 percent of Democratic voters showed up on primary day.
https://www.wdde.org/wp-content/uploads/2010/09/voter_turnout.jpg