if they are trying to target the average American, then 5 figure bank account screen shots are ludicrous
Not really.
It's done for the same reason you see healthy, beautiful models in all advertisements - even ads for things like prescription drugs to treat debilitating diseases. If they show an ad with someone who LOOKS like they're dying, people are gonna look away and try not to see the ad. If they show an ad with a beautiful model, people are gonna think unconsciously "Hey if I take this drug it might make me beautiful too!". Obviously that's absurd, but it still has an EFFECT on you.
Same thing here. If they showed account balance of $-136.87 (overdraft), even though it's more realistic for the 'typical' consumer, people won't respond as positively. By showing account balances of 5 figures, people will think to themselves (consciously or unconsciously), "Hey if people that have 5 figures in their checking account use Bank of America, maybe I should too - it must be what people who are smart about money use!"
It's basic marketing, plain and simple. Emotional appeal, nothing more.
"Sell the sizzle, not the steak."