Because long story short there are way more counters vs axis mgs than there are vs the maxim. Add on top of that the faster setup time of the maxim and youd be able to attack move to victory right into the axis base with a maxim blob like in the old days of maxim spam glory.
There were a lot of things that made maxim spam viable in the maxim spam glory days. Squad spacing was wide and limited grenade damage, turning speed was high, ostheer sniper had low health, low small arms fire DPS led to increased benefit of suppressing squads over killing them with rifles and limited the effectiveness of flanking the maxim.
All these things have changed. The turning speed of the maxim was reduced, effectively making it less effective than the MG42 at targeting squads that attack from the front (smaller arch), but more effective at targeting squads that did wide flanks (faster repositioning). Squad clumping was added in, making the maxim vulnerable to arty and rifle grenades (the #1 reason why you hardly saw any maxims made last patch). The Ostheer sniper was buffed enormously. The result was that maxim spam was dead, and that maxims in general were hardly seen as people preferred to just make more conscripts rather than with a HMG that could be rifle grenaded to death from the front with ease.
The maxim _was not_ a good unit last patch, and I do not see why it should remain that way when other HMGs are actually made very potent for once. Things like fast pack-up speed are useless* when the MG can't even suppress 2 squads walking hand-in-hand towards it.
*not completely useless, as you can retreat faster from those squads who walked right in front of your HMG. Oh joy, what an advantage.