User blog comment:Xilinoc/Ch. 686 - Death & Strawberry (End of Bleach reMIX)/@comment-24577094-20160818150410/@comment-24531362-20160818203526

Maybe it's a symbolic thing. Rukia was adopted into the Kuchiki family, and holds a lot of pride in this, the only family she's ever known. Her keeping the name makes a lot of sense.