After Civil War and everyone thought Steve rogers was dead Thor goes to his grave and resurrects some random person (Steve wasn't in the grave). I think they had to pray to him or something in order for him to bring them back but in another issue he accidentally killed an innocent and ressurected him.

Since Thor has that kind of power why does he let his friends stay dead ? Does that make him a bad friend

That doesn't make him a bad friend. Reviving people isn't a normal thing and perhaps people don't want to be revived? Thor got pissed when he found out that Ragnarok was a cycle that was repeated over and over again because it meant that every time an asgardian died it was for nothing, so it would lessen the value and meaning of their death if you bring them back all willy nilly.

or it would put more value on life. To be bolder next time stronger and try change it all. Half full half empty I mean the after life of the Norse is all around this whole theme. Fight all day and die and be brought back and eat at the table of Odin. Why is this new to Thor?

No. Thor loves his friends.