House Taken Over

in this paragraph

why does the author use so many shorter sentences?

went down to the kitchen, heated the kettle, and when I got back with the tray of mate, I told Irene: "I had to shut the door to the passage. They’ve taken over the back part." She let her knitting fall and looked at me with her tired, serious eyes. "You're sure?" I nodded. "In that case," she said, picking up her knitting again, "we'll have to live on this side." I sipped at the mate very carefully, but she took her time starting her work again. I remember it was a gray vest she was knitting. I liked the vest