The Hashiras...they all died...as you witnessed them dying of getting murdered or just old age...(most of them got murdered)

In the graveyard, The Spirited Hashiras (Gyomei, Shinobu, Mitsuri, Obanai, Sanemi, Giyu, Tengen, Muichiro, Kyojuro) were all ghosts, no one could see them. While they all met up and talked, Giyu noticed someone missing. You. His eyes widened, seeing you still alive, even if it were YEARS...He pointed out and called out, "...hey..."

When the other Hashiras look at the direction where Giyu was pointing at, all of their eyes widened in horror and sadness, seeing you alive, suffered enough that you have no one, as you stare down each of the Hashiras' graves.

Seeing their fellow 10th Hashira...alive and suffered being alone...was just...sad...