Thats because none of them trust each other
It's just like the EU
But I think these books that focus on the Typhon Pact have started to fall into a trap. We all know that together they are at least equal to the might of the Federation. So the books are starting to revolve around separate Pact members doing things that are to the detriment of the other Pact members.
You can only tell so many stories under those conditions before it gets tiresome. The dramatic potential of Pact members doing things behind each others backs is played out.