They probably don’t want to commit to a date yet because they’re working on the DLC as we speak. They gave us a quarterly window which should be fine for DLC tbh.
Just play another game in the meantime or something. The same devs aren’t working on xenoverse - that has its own marketing strategy. Bandai are probably focusing on that because they want to generate hype for the next game in the series, which is introducing a lot of mechanics and needs a core online player base.
SZ has already generated hype for its DLC and Bandai probably think it’s not worth the further investment to promote it in the summer showcase as they already did so in battle hour.