Analyzing Attack on Titan. Season 1

Attack on Titan is based on a legendary manga series by Hajime Isayama which started in 2009 and only ended in 2021, seven years after the show premiered in 2013. This is an important factor which should explain us a lot.
In this story, humanity almost got destroyed by the horde of horrendous human eating Titans. Titans are huge and resemble humans in an uncanny way. The survivors of the catastrophe built three huge walls called Maria, Rose and Sina to defend against the Titan. For one hundred years humanity lived in relative safety from Titans. Except for Survey Corps soldiers who regularly go outside the walls on expeditions. And not all of the soldiers return from their ventures into the enemy territory. Overall, life was relatively safe within the walls but one day a mysterious Colossus Titan and Armored Titan appeared in Shiganshina, the town where our main protagonist Eren Jaeger lives with his parents and his adopted sister Mikasa Ackerman. Armored Titan breached the gate, letting a horde of titans in. As a result, Eren’s mother died. Eren, Mikasa and their friend Armin Arlert decided to enlist in military training and become members of the Survey Corps. Eren to avenge his mother and kill all the Titans and Mikasa to protect Eren and keep him alive.