I have absolutely no data, but I wonder if a decline in public decency is also playing a role. It isn’t hard to find videos or articles of service workers getting harassed or physically attacked by customers.
So your idea makes sense.
I don't think it will. I know plenty of people who've worked retail and still treat others like trash.
That being said, I still agree that empathy in general seems to be trending downward and my assumption is that online life makes it a lot easier to dehumanize other people which makes it easier to treat people like shit.