Our group did a total inventory to look at all the Influence cards across all the expansions (mostly for balance checking and trying to get a feel for the influence cards that were fun to use and balanced).
We noticed that there were only the 2 forced missions in the core set ... and that's it. There's a chance we're missing one, but all the other agenda missions are optional side missions.
Why do y'all think that is?
"Surprise! you're playing this mission no matter what now" is a very unique concept ... so why wasn't it ever revisted?