Because it's impossible for the community team to balance them before putting them in the game.
I'm sorry, I have no other way to ask that - are you that stupid or that naive to believe there is any way to balance 5 man dual flamer unit?
There is a reason why every single unused concept unit outside of this one, T34/85 ace(red banner dual T34/85 call-in) and T34 osttruppen(shit tier T34/76 that's more spammable then T-70, you can see it in ToW) made it to the game.
These three go completely against what CoH2 is/tries to be for last 4 years.