First, to forestall any potentially unhelpful suggestions, I am fully aware of house rules and how to basically make the game what I want it to be, but this is a question that maybe goes beyond the what and addresses the why.
So I was going through Miskatonic Horror, and I noticed that the Injury and Madness cards are to ONLY be used with Dunwich Horror. Why is that? I always thought the Injury and Madness cards were a pretty good idea. Why does the game want me to lug out the Dunwich map and play with that, too? From what I see, it's not integral to that expansion as much as, say the Exhibits are to Dark Pharaoh or Blights are to King in Yellow.
I haven't played with Lurker at the Threshold yet, but I like the idea of the Relationship cards. However, the rules say "These cards are only used when playing with" Lurker. Why is that? Again, I may be ignorant of Lurker, but is that all there is in that little box? So if I am playing with Relationships then I am ipso facto playing with that expansion?
It appears you can play with Nodens or Hypnos in play, but that doesn't mean you MUST incorporate Kingsport.
So, if there's a real reason why I can't incorporate these things, I'd like to hear about it.