Pretty much everything you listed made solid progress during Obama's tenure. I think people are concerned about the
current direction.
Sessions rescinded an Obama-era rule on marijuana enforcement[1].
It's entirely likely that abortion will be outlawed in 20 states within 18 months.
Income and wealth inequality continued to rise during Obama's tenure and last year's tax cut shows no sign of that stopping. One could argue that the inequality is natural in a liberal environment, but one can also argue that the rules are stacked in favor of the wealthy.
Quite a few states are making it harder for people to vote, especially those who have lower incomes or belong to minority groups.
Partisan gerrymandering (by both parties!) subvert the will of the people.
Finally, false attacks on legitimate press as "fake news" and baldfaced lying by government representatives subvert the press's ability to be a watchdog on the government. That said, the press still has its Constitutional freedom, so I don't want to overstate this point.
Regarding prison population which "has been declining for about eight years" and the US's broad support for ending minimum sentencing... that applied under Obama. That does not apply so much under the current Attorney General[2].
I think there is good reason to believe that the US is becoming less liberal (in the liberal democracy sense) since January 2017.
(Also, to be totally clear, I'm not saying it's anything like the dictatorship that has arisen in China today!)
[1]: https://www.washingtonpost.com/world/national-security/sessi...
[2]: https://www.vox.com/policy-and-politics/2017/7/11/15955570/j...