>>49596264
Because it's cool.

>>49599533
There is a recap movie (Rondo Rondo Rondo), which tie-in a bit better to the sequel movie thanks to additional scenes and also a "season" of short comedic episodes featuring the cast introduced by the game (Siegfield, Rinmeikan and frontier) called Conte all starlight.
If I remember right there is cut where someone spliced the additional movie scene into the first season.
After the sequel movie there is the VN, El Dorado which is pretty much the conclusion for the Kukugumies.

If you want more content there is also Arcana Arcadia, the final story and culmination of the mobage, it's pretty nice despite being trapped by its origin.
https://www.youtube.com/watch?v=_98ndFBcDic