Not teching to Major was incredibly efficient. You could go both Lieutenant and Captain, getting the full suite of tools and both combat officers. You'd also save a ton of fuel in the process, allowing you to rapidly amass critical mass of M10 tank destroyers.
It was so good it choked out the other USF strategies, so the M10, the Flame Hetzer, the Ostwind and the KV-8 got tied to tech in DBP.
Lend Lease's M4C Sherman got tied to tech the patch before that.
Again so what. USF got a full tech tree, plus could amass a cheap and effective AT unit similar to the STUG III, that almost sounds like they'd be on par with OST Heer! Can't have that!