Because its more fun to trade cuz your gonna get different ids for the Lotto tickets in jubilife city.

My team when traded:

Palkia lv 76
Empoleon lv 53
Tentacruel lv 49
Palkia lv 55 or 54(i forgot)
Infernape lv 90+ by now cuz i gave it back
Staravia lv 28