The spawn of the missions is random and there will be periods of times where missions come and go for lack of a better term. This is how you'll have six or seven high rise fires back to back and then none for a long period of time.
The missions themselves haven't been removed from the game, you just haven't reached the spot in the mission spawn table again where you'll see those missions.
If that is what you think ok...but I can tell you it has been well over 2 or 3 months since I have had any of those missions.