Lets give USF dodge truck in T0 as well, because reasons.
Thats why.
Unit is not supposed to be part of core army and it shouldn't be there.
If someone is so desperate for HMG, then either pick the doctrine with it or play Ost.
Each army lacks something, some have it in the doctrines, but there isn't reason why it should be made stock, no matter how many people cry or scream for it.
Especially since OKW already have early game suppression platform and don't need it for late game because they have multiple units with suppression capabilities already.
OKW gets completely wiped off the map early game, that is the gap the MG34 is should be filling. Kubel does not do this because:
1) terrible pathing and stupid unit design, becoming useless after 5 minutes
2) It also occupies a sturmpioneer squad. Getting early vet on this unit is incredibly important, if you don't they will drop off even harder than they currently do. Kubel needs babysitting, and sturms don't get vet from repairing and capping. Kubel will die anyway, so you are losing pio vet for nothing.
I don't think it is disputable that OKW early game is currently terrible. This is because of bad volks, but also because of the lack of proper suppression. The kubel simply does not provide in this regard.
Effectively, as the situation is now, against some factions, you get locked into 2 doctrines, fort being ok in some cases, luft having good call ins, but 2 useless abilities and one extremely situational one.
Most OKW suppression isn't that good.
-Kubel, as stated, as lots of issues.
-Flack halftrack is bad because of the engine bug, but also because hard counters are so readily available against it. Rushing t70 and stuart is very good against OKW because of their poor early game presence, meaning you can get away with it.
-LeiG should have its suppression removed, but is nevertheless not a substitute for an HMG team.
-Flack halftrack doesn't count, its a stronger version of a bunker (which OKW does need pretty badly though because otherwise it simply has no way of holding territory). However, it does nothing for you in fights, so it doesn't really count. Just like I wouldn't count ost bunker as a proper form of suppression.
Sure each army doesn't need to have the same unit as stock, but this is a strong instance of the contrary. If anything, core MG34 promotes different builds with different unit interaction, making for more interesting game play. It would be quite interesting, for instance, to use an officer with the MG, and I think it would make that whole doctrine more viable again (outside of spamming fusils, which I personally found to be ineffective recently with allied vet buffs). Don't really see how you can argue against that.
Implementing the MG34 is hardly game breaking. It is already available, and those doctrines do not suddenly make OKW more op. If the Mg is generally buildable, it will merely make more build viable. Reasons like "okw already have enough suppression" just completely miss the point. The options OKW has are pretty ineffective.