It literally doesn’t. Like yeah, it sticks together into clumps, but you can easily break them back up into shreds with your hands. Source: I’ve worked a bunch of pizza jobs, both on the high and low end. Guess what, it literally is not cheaper to pay the labour for someone on staff to shred it, at least here in Australia where we pay real bloody wages.

Also, to the OP, “pizza mix” cheese usually is your best bet. They’ll sometimes label it as “meltable mix”.