Because schrecks are just straight up better. What about RE and Engineers? They still aren't going to be effective ai with 2 bazookas.
With volks getting a schreck is just obvious, you will do it on every squad for no drawback. Upgrading dual zooks or duel piats on every rifle and IS is just stupid and will get you walked over because you have no bars/lmgs.
Bazookas are still very effective and very strong AT weapons. REs and Engineers aren't effective AI in the first place so you can upgrade them to AT for almost no drawback.
You just upgrade some squads with LMGs, some Bazookas/Piats and some with both or just upgrade according to whatever you enemy has. You are trying to make it sound like picking Bazooka/PIAT is a death sentence for USF/UKF when that is not the case at all. A rifle squad with a M1919 or BAR and 1 Bazooka will smash a Volks schreck squad AND be potent AT considering they have snare as well. Get a few of them and some REs with Zooks plus Cpt/Lt etc and you have death blob far more powerful than anything OKW can muster. You are trying to justify absolute hypocrisy when it's obvious that Rifle blobs can walk all over OKW much easier than Volks blobs can walk over USF (note: Volks can't).
Let's compare Schrek Volks and Zook Rifles
Volks: 1x Panzerschreck, 4 men poor AI and flame nade
Rifle: 2x Bazooka (2x Bazooka > 1x Panzerschreck), 4 men decent-Good AI and grenade, snare and smoke.
Of course the Volks are much more OP.