clean history wont prevent you from getting a loan in the usa, it just prevents you from getting a big loan at a low interest rate. Smaller amounts won't be much of a problem if its a clean. Also, bad marks are removed in time just like anywhere else.
I think the reason why clean reports may be a little bit more of an issue in the us than elsewhere is because of how easy it is to get an kind of loan or credit and how uncommon having a blank credit score can be as a result. Between student loans, credit cards, car loans (atleast cheaper loans for used cars) etc its pretty unlikely, by the time someone goes to try and take out a big loan, like say for a house, that they would have zero credit history or not have someone like a parent cosign who also has zero history (if someone cosigns it goes on both people's credit history) And, businesses, looking for any excuse to avoid risk on an investment, would be less likely to give a big loan to someone with no history when there are so many people with good credit history to still make plenty of money.
All that said, credit cards seem quite a bit less common than they used to, especially since debit cards became a thing. Most people i know, myself included with credit cards are either for business expenses that are paid off immediately, or for the extra safety provided by the ability to charge back on purchases that debit cards don't often provide.
Its a problem for sure. A large portion of the obese tend to be poor people who are working 40-80hours a week with half and hour to 2 hours commute every day who possibly have kids to take care of and may or may not be a single parent household, fast food isn't the cheapest option, but its the cheapest option they have time or the energy for. Also, since most fat food (and most other processed or prepared food sources) know how addictive high calorie and high salt foods can be they will happily take advantage of under educated and over stressed people by cramming as much as they can afford into their food. That of course doesn't apply to everyone and plenty of people who have no excuse are still fat but that applies to a rather large chunk of the overweight people. That also exposes a whole bunch of other issues that need to be addressed as well.