Of course he didn’t want the lightsabre that he’d already given up. Wouldn’t it be even weirder for him to be all “oh, thank you so much for giving me back the sabre I purposefully discarded after I tried to murder my nephew and turned him away from the light, it would look great on my wall!”

That was actually Anakin’s lightsaber, the one given to him by Ben that he lost in the duel on Bespin, that most people presumed was lost forever after having been shunted out of a trash chute into the atmosphere of a gas giant. He didn’t make a conscious decision to give that one up, though I understand his reluctance to accept any lightsaber in the first place what with everything that happened that we learn about throughout the movie, but the casual toss-over-the-shoulder for laughs was pretty inappropriate considering the tone of the same scene at the end of 7, explicitly framed in such a way implying that Luke had an emotional reaction to seeing either Rey or the Lightsaber again.