After the Wagner Act of the 1930's, the low paid mostly minority service workers on the railroads rapidly unionized and got collective bargaining agreements, so by the 1960s, they were probably being paid more. And back then, even ununionized food service employees were being paid enough to live on, yet it was still customary to tip them. Tips were an expression of appreciation for the service, not a way to have the customer subsidize a living wage that the employer should be providing in the first place.
As far as Amtrak employee compensation, according to Glassdoor, Average wage of an Amtrak service attendant is $22/hr, or about $44,000 annualized (assuming they have full-time hours). While this is above the median individual income of the country, it's not that much above it, and I'd hate to have to live on a $44,000 annual salary, even with the other employment benefits. Maybe if I was in my 20s, and I knew that there was a career ladder that would have me earning a lot more than that...