why are the orks all so lightly armored?

ironjawz player coming from aos, i was thinking orks would be my first army (they still might) but i was reading through their rules and almost the whole army is wearing t-shirt saves, and even their more elite guys like nobs only have 4+ saves, the only ones with a decent save in the whole army seem to be the meganobs who are wearing, as far as i can tell, lego bricks and calling it armor. they also dont armor their mounts, what the hell? those squigs are gonna fall to the first stray bullet to come their way without a bit of armor

why are the 40k orks so averse to armor? the longer you live, the longer you get to fight, seems like a no brainer, even for a race without brains.