There's little or no trend among people without college degrees, but a downward trend--that is, more support for redistribution--among college graduates. There are some year-to-year ups and downs that apply to both groups (partly related to the party of the president), so if you look at the difference the trend is even clearer:
The drop in 2016 is unusually large--if you fit a trend from 1978-2014 and extrapolate to 2016, the standardized residual is -2.63--but the trend is clear even without it. That is, there has been a gradual decline in the the difference between the opinions of more and less educated people. Why? One possibility is that it has to do with economic trends--the income gap between college graduates and other people has been growing since the mid-1970s, so educated people feel more generous or more guilty, and more inclined to do something. Another is that it's about politics--more educated people have been shifting towards the Democrats over the same period. Regardless of the original reason for the shift, once you start voting for a party, you'll tend to have more trust in its leaders, and adopt more of the positions usually associated with that party. I'm sure there are others, but those are the ones that occur to me.