The whole point of putting the mortar in the game was to diversify USF's opening. If it's behind tech then there was no point of adding it in the first place.
Let's be real, Relic hasn't diversified anything for USF. Pretty much every player you see goes 3x riflemen still, with or without the mortar that would only be slightly pushed back in timing if ti was added to LT. Not to mention 99% of people only use Heavy Cav or Tac Support, and that's not going to change anytime soon.
If they wanted to diversify things that ship sailed awhile ago.