I'm not going to my great grandfathers funeral
What is your reason for not wanting to attend his funeral?
He died alone and without anybody
It is customary for even people who did not know the dead to show up for a funeral. It is a family obligation and might help you grieve and bring closure to losing him.
It's his fault for directly dying alone. Why should I care?
You should care because he was your great grandfather. You should want to attend his funeral and celebrate his life with the rest of your family. Blaming him for dying alone is really focusing on the wrong thing in this situation.