The Mages Act As One

From Kokorodatabase

Since the majority of mages are roleplayed by Saica, there is a tendency by this authoress to have her mages to do everything together, whether it's to sing karaoke or just fish in the lake on the weekends.

Mainly, though, this running gag refers to the joint gifts that the mages give to various people. There are exceptions, such as a relative's birthday (like Shuugo's or Jishou's), or just pure dumb luck. This could basically be pinned down to "lazy authoress".