If all Bezos cared about was having lower taxes for billionaires he could have simply hired a bunch of people who believed in that and had them be the editorial board, and they would endorse whomever he wanted.
The fact that he had the editorial board he had (1), which wrote up an endorsement of Harris several weeks ago for his approval, and then he suddenly decided it was better not to endorse at all? That fits cowardice much more closely than it does pure economic interest.
This isn't government censorship, obviously, but do remember that the only point of the Editorial Board is to write opinion pieces and have them published in the paper. That is their entire job! They aren't reporters, they don't go out and ferret out news. They have opinions, and they write them out and get published in the paper. And they wrote out an endorsement of Harris, and suddenly it was announced (to the board only slightly before it was announced to the rest of the world, according to published reports) that they weren't going to endorse for President any more. That's a fact pattern that leads one strongly to Jeff Bezos' personal cowardice as the most parsimonious explanation.
1: At least before the resignations come in, I expect the board to be very different in a few weeks.