Every game has different game mechanics so that not every game needs something another game has just because it works so good in that game. I always wonder when people open threads like this. Same with the 6vs6 "problem" since it doesn't look like a problem in Titanfall (32vs32 would be a problem in this game) and even games which are only 1vs1 can be good if they are specifically made for this.
It could be very unbalanced if Titans could kill everyone behind walls if they really didn't implement it. They would have to make Titans slower or less agile so that Titans wouldn't totally rape normal soldiers.
So, I'm pretty sure the reason why it doesn't have it is balancing and nothing else. And if the final game will have it then also because it is better for the balancing.
