So, because Hamlet and almost everyone at the end of the play died. Hamlet felt content. He felt that his tragic flaw was finally overcome and he was able to avenge his father by killing Gertrude's new husband. Sadly it was resolved by everyone getting stabbed, poisoned, bludgeoned, amongst other things. Hamlets attitude was per say, (Just saying kinda what he would be feeling/thinking this is not an actual quote) "Finally, I avenged my father. I can die and piece and this kingdom will be safe under someone else reign (not knowing that fortinbras is about to invade denmark and mess all kinds of things up)
Hope this helps! Comment if you need anything else my friend!