Siver was ranked about 6 until he lost to Cub (got caught in the third but was winning that fight) and was instantly dropped down to about number 15.
Siver has 8 wins out of his last 10 fights and his losses have come from Cub and Donad Cerrone. Siver has fought as high as 170, was at 155 for awhile and then dropped to 145.
As others said, when Conor was looking to get a fight, everyone else was lined up and booked. He had the choice of sitting on the sides for an unknown amount of time or taking a fight and staying sharp.
Looking at it now he could've waited and be facing Aldo in another month or two. But had Aldo lost, that would have delayed it due to the rematch, the threat of injuries from any given fighter, etc...
Can't fault Conor for taking a fight even if Siver isn't known to most bandwagon fans.