It isn't just another launch, every future launch with this same rocket is now an experiment. It can't have the same reliability rating because a second launch hasn't been tested and these aren't freshly machined parts. Every piece in the rocket has experienced a level of wear and tear that previously launched rockets didn't have. Maybe it's exceeded the amount of cyclical stress it can handle? Who knows, but most satellite companies wouldn't pay the same for a re-used (never before been re-used) rocket as they would for a brand new rocket because of the increased risk. I would not be surprised if they did in fact give a discount to the payload of anyone who rides this same rocket. If they don't give a discount the only reason someone would purchase a spot on it is for the prestige.

Note: The never before been re-used part is probably the most important factor here. Once they have re-used rockets a few times they'll have a reliability factor for these situations.