In order to determine how many copies of Flash Point Fire Rescue: Call of Duty have been pledged for, I need to have all the pledges be for the kicsktarter expansion only.
That is why add-ons are done after the project. And while I know YOU wouldn't add $ for add-ons when asked not, I am sure that some people would.
And if you really want to know the add-on prices, please see the project updates.
So not listing add-on prices is done to prevent people from breaking the process. Ultimately it would be great if kickstarter added such functionality but for the time being we need to work within the system constraints.