because it has a fire rate of 25-28 per minute with a medium rammer, does 85~ damage which isn't much but annoys everyone and taken as DPS is VERY high but most importantly has excellent penetration for its tier and fire rate.
Oh and its damn accurate.
You can penetrate tiger II's with it if you aim well and its a gun that rewards skill- you HAVE to aim carefully against top tier mediums and tier 6+ heavies but you have the mobility to manouvre to where you can damage them. Aim for the weak parts of the turret and such is your fire rate you can mess up his gun by getting gun jammed and damaged results.
The gun is probably due a nerf tbh