Because replacing Tactical Movement with an assault type ability that doesn't involve sprinting would allow to keep the best of both worlds. About 49% of people still voted for Panzerschrecks after all.
And an assault ability (Tactical Movement) wasn't in the original proposal anyway. It was added to replace the proposed HEAT shells (would've been problematic with Tiger and doctrine power level) in the spirit of the offensive theme. Any assault type ability can fit that spot.
The Tiger Ace (in its current state) would have a much less distinguishable role over the King Tiger than the regular Tiger has. The TA has 1280 hitpoints (same as KT), less mobility than the Tiger and it's nearly as expensive as the King Tiger. It even has the Spearhead ability.
The regular Tiger on the other hand is a cheaper, less tanky but more mobile/aggressive alternative to the King Tiger that stands out much more.
Well thats what happens when you have those 50/50 cases. it seems to me the double shreck thing is just a no win scenario (many want double shrecks but many hate the idea so be ready for even more complains after the patch is out) but if the team really want to keep them it was worth making that clear.
If i may suggest, assault and hold ability could be a good replacement (good assault ability, no sprint, can work with smoke) and like I've said many times please bring back the IR stgs. Panzer commander is good for elite armor but the stgs even in spec ops are quite a forgotten ability. I'm all for good assault obers play along with soviet paras, panzer grenadiers and cheaper rangers.