It looks like the second series is also getting a "Starter Pack", which doesn't come out until May 3rd (globally). It advertises the second series on the side and has series 2 battle cards inside (just like the first starter pack, the four character cards are exclusive to this pack, with series 2s on the cards).

Considering how much the first starter pack is shelfwarming here, they probably need the extra time before releasing the second starter pack.