I think it reflects poorly on Luke's character that he could simply see the bodies of the two people who have raised him from birth brutally murdered and not even an attempt at burial
We have no idea from the film whether Luke buried his aunt and uncle or not. The scene shifts to the Death Star right after Luke finds their bodies in one of the most dramatic transitions in the film. We can only speculate that it probably would have been unsafe to hang around too long at the Lars residence. Luke was lucky not to have gotten picked off or arrested just coming back to make sure they were OK.
Okay, that last part does sound logical. But the real problem is that we are not shown that the two deaths have had any impact at all on Luke's life. He goes on like they're forgotten almost immediately.
I don't assume stuff in movies/TV. If I don't see it or hear it or it is not pointedly implied visually or audibly, I assume it didn't happen. But we are beng asked to conclude that Luke does care for these people but neither he or the movie shows that to us. One little line of dialogue could have done it. Just a mention of them by Luke followed by a gaze off into a bulkhead or something would have said a lot. I was always left wondering if he cared for these people.