It's love for Mirka. Submissive love. If she orders him to play on wheelchair he will. Anything she tells and she'd tell him anything to keep the records and the mountains of Rolexes and LV handbags coming with them.
He's only still plays because he's desperately trying to cling onto his records, but it's too late. Not even pathetically vulturing slams over Hewitt, Roddick etc. for years is going to help him top the all-time tally.