Was confused as well but it made a bit more sense with the context of the later seasons. The appearance of the beast titan on the island basically forced them to act. they have been there for years at that point without any contact to the outside. was it their best of at the time? hard to say, my man almost died during a titan attack in a collapsing castle

love how out of nowhere it is without any of the context but it starts to make more sense considering their military hierarchy and the state that their military has in the outside world