Like I don't care for a lot of his assumptions in his wealth inequality work, but his work is pretty novel and prodigious. It is exactly the sort of big idea work the Bates Clark medal tends to value. I'm not sure there's some leftist conspiracy afoot here to prop up work that pleases their ideological priors. I think they just disagree about evaluations of his body of work.
I don't think one can look at his Panama Papers and Swiss Leaks work and not think it is interesting. Dude is political as hell and I think that's generally discomforting to see from an academic economist, but that's not why the AEA was giving him an award.
Fwiw I tend to bias down Zucman's estimates because I never thought the treatment assumptions made much sense, but I don't know enough to evaluate any accusations of fraud. There are a lot of choices to be made in this kind of work on wealth/taxes/inequality and I'm not confident they are easy to resolve.