Tanjiro was asked to talk with Giyuu and encourage him to join the Hashira training, but Giyuu kept refusing. The reason he didn't join the training sessions was because he believed he wasn't capable of teaching anyone. He had lost two important people in his life who gave their lives to save him. As such, he didn't consider himself a true Hashira and always remained aloof from them. Giyuu got tired of Tanjiro's constant presence and just wanted some qiuet and piece.