Just the axis response to massed infantry(particularly elite) being used by the allies at the time.
Fluctuations in the metagame. They always happen - allies are likely to begin using more quads/M8s to counter - panthers will begin hitting the field : AP rounds will become more prevalent, axis will shift to more light vehicles to deal with AP rounds ATGs, allies will go for elite infantry with HHAT again and so on and on and on.
the rangers are usless against them
you can try rushing the wolks but they get suppressed way to easy after getting a grenade gets on them
you can try using flamers but the grenades just kill half the squad the same second they stop
you can try running but the grenades will reach them if they do not use sprint
you can use sprint but as soon as it stops they move so slowly they cant get away from the grenades
you can flee but then you are just wasting them so you could just as much let them attack