Also, I think modern society is making people a lot shittier, especially if they live in cities without extended families.
In smaller communities, your reputation was everything. And psychologists have shown that reputation is what makes people make moral behaviours. This was fine is small villages where everyone knew one another, but in bigger cities this is impossible and shitty people can keep going around and staying clean with their reputation by just not being around people that would know them.
Also, if there are too many people around, we get used to people that we don't bond with, when in older times every human we knew we bonded with (or were enemies with, traded with and say only once, etc).