26″ entries are at an all-time low. Note that in 2013, the FCI Agility World Championship was held in South Africa, and the AKC decided to fund a team for the European Open instead.
For comparison, here are the entries for the other height classes during the same time period. The heights trend together—but not with the 26″ class (compare the chart below to the chart above).
Looking at the percent change from the previous year, we see that the 26″ class has always been volatile. However, this year marks a dramatic 40% drop in entries superimposed on the two-year drop in entries across all heights. In addition, the 26″ decline actually began in 2010, so there appears to be more at work here than the international trend of dropping 26″ to 24″ at major competitions.