I think people are missing the point.
Yes, you can pilot a mech if you wanted, and that's because the control interface is levers and buttons. But optimally you wear a suit. If the pilot's cabin's structural integrity were compromised the sudden decompression would cause the pilot's eardrums to blow deafening them, blood vessels in their eyes to pop blinding them, and the air rushing out of their throat would damage their vocal cords probably rendering them unable to speak even if they had the air to do it. And that's assuming gravitational forces remain intact otherwise you could risk a syncope episode even if the hull is undamaged which means the mech is defenseless and probably careening through space (or a populated area) out of control. Pilot suits are defense against that, often supplying supplemental oxygen, maintaining pressure support, and even adding constriction to lower extremities to prevent blood from pooling away from the head. And that's what they offer now, who knows what they could offer later (like modern's suits for example). So like wearing a hardhat & steel toe boots in a construction area: You don't need one to walk around, and certainly there is always that one guy that argues it's safe or he'll die so why bother, but you'd be retarded to pass up the chance to use them just in case of an accident.