Aldo is ranked #2, behind Ortega, he already beat Mendes & Edgar multiple times, he just finished Stephens, and Moicano fights this Saturday. Cub is the highest ranked available matchup that makes sense.
It's also a decent matchup to see where Aldo is at. If he's still an elite level contender then Cub should be a bit of a soft touch, because he's a standup guy that does nothing better than Aldo on paper. Could be a showcase win, which could then set up a title fight if Ortega wins. If he loses or barely wins then it might be getting close to that time for Aldo.
Also he's been facing nothing but title contenders for years. Giving him a soft touch while they figure out what's gonna happen with Max and Ortega is smart. Possibly set him up for one last run at 145