According to Nintendo of America’s Twitter page:
Players are visibly confused in Splatoon’s plaza, many Miiverse posts taking one of two positions: outraged at the delay, or trying to inform other players why the event had to be delayed. Some players are still hopeful that the Splatfest will be resuming shortly, writing posts such as: “No matter when: Team Cat will win!!!!!” or “Nintendo just wants to give Team Cat a chance to practice!” A select few, however, will be quite upset due to their Splatfest Tees being taken away as one player I saw this morning wrote:
If delaying Splatfest was a necessary evil, then players can only hope that there will be no issues at all when it finally arrives. Until then players should keep practicing on the new Splatoon map: Bluefin Depot, a map some players will recognize during Octoling matches in Single Player.
Stay strong fellow Inklings, Splatfest will return! Until then, Stay Fresh!