Because it would call for slower pacing which are fine for books but doesn’t translate as well in terms of film. Still a great idea though.
Pacing only comes down to the director’s taste. You can totally have both espionage and fast pacing in movies (think of every James Bond film).
That works for that franchise, but there are other factors in SW films that need to be adhered to and blending them together so that the espionage is substantial could be troublesome. Also again I think this would work better as a book due to the fact that they’ll be longer waits for things to happen, sneaking around more exposition, long drawn out conversations etc. Also the aspect of a Cold Wars sounds like something that would happen in a prequel novel rather than an actual Star Wars film.