This is the reason why Ethan had Arceus.

HE HAS CELEBI AND LEGENDS MC SENDS THE BALL(Arceus) THROUGH A SPACE TIME RIFT (MYSTERY GIFT) WHICH GOT INTERCEPTED BY ETHAN AND CELEBI.
>Why didn't he send it to the Sinnoh MC's

BECAUSE HE IS THE SINNOH MC WHO GOT SEND BACK IN TIMEEEEEEEEEE. That's why the azure flute never being officially released makes sense.

AHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH