Got this from Wikipedia:
The armored tub ranging from 5-12 mm (0.2-0.5 in) in thickness and enveloping the engine and the cockpit, could deflect all small arms fire and glancing blows from larger-caliber ammunition. There are reports of the armored windscreen surviving direct hits from 20 mm (0.79 in) rounds. Unfortunately, the rear gunners did not have the benefit of all-around armor protection and suffered about four times more casualties than the pilots.
Thanks to the heavy armor protection, an Il-2 could take a great deal of punishment and proved difficult for both ground and aircraft fire to down. One Il-2 in particular was reported to have returned safely to base despite receiving more than 600 direct shell hits and having all its control surfaces completely shredded as well as numerous holes in its main armor and other structural damage. Some pilots favored aiming down into the cockpit and wing roots in diving attacks on the slow, low-flying Il-2 formations.[16] Several Luftwaffe aces claimed to attack while climbing from behind, out of view of the rear gunner, and aim for the Il-2's non-retractable oil cooler.
But, like earlier, if the Pintle guns are uber, there is likely a reason.