The liberal endorsements probably have to do with him denouncing some Trumpian comments from the CEO of Under Armour (one of his sponsors) and his refusal to support a travel ban. But that seems like the bare minimum effort from a person who's planning to run against Trump (on either side of the aisle). Shit, Ivanka Trump has been tougher on Trump than that, and she makes her living monetizing his farts.
The Rock's actual record is even more obtuse. Supposedly, he is now a registered Independent, and he refused to endorse either candidate or even reveal who he voted for in 2016. One time he appeared at both the Republican and Democratic National Conventions in the same year. Flying right down the middle is great if you're a professional bowler, but you can't answer every debate question by smiling and saying, "I love America." Or maybe you can, but ... well ... you really shouldn't.
Sigh ... people would probably vote him in for it.
Even with social issues, he walks a fine line. When the Hulk Hogan tape came out (the racist one, not his butt one), The Rock expressed that he was very disappointed in Hulk "Mr. America" Hogan, but added "it's funny, it's one of those things where, and not justifying what he said, but we've all talked trash, especially in private." Damn, he won't even denounce the N-word!? Dropping that bomb is just locker room talk now?
This hardcore devotion to staying exactly in the middle of every issue is a winning strategy for an entertainer who wants all of America to love him, but not for someone who needs to make decisions once in office. He'll have to take positions on healthcare, immigration, etc. And one side of the spectrum will be very disappointed, unless he makes his announcements mid-song in a Moana sequel.