Beating guy who isn't even willing to fight top contenders in a smaller division is not a complimentary win compared to elites at 155 that he wants to fight. Khabib is a real warrior who wants the best. He isn't going to ruin a fight in his career to fight some other guy from a smaller division who isn't a warrior that has a reputation for ducking opponents from his lower weight class that recently got drilled in 13 seconds in the most embarrassing title loss in MMA history.
Its a no brainer as to why the fight does nothing for him. It isn't even a real match up any way. UFC is trolling Aldo and trolling all the idiots who actually believe that they'd put Aldo's weak ass in a potential 155 interim fight. They'd be better off giving Frankie Edgar a shot if they were going to do that. He is a much better draw, and will fight anyone unlike Aldo.