Well, because my seeing his taxes won't do a damn thing to improve my life, nor would it have any affect on how he runs the country.
Ok, but that didn't answer my question. My question was "Why wouldn't you want to be able to see as much of your leader's finances as possible?"
Don't ask yourself if you want to see candidate Trump's tax returns Ask yourself: when AOC (or whatever politician you hate the most) runs for president, do you want to see her tax returns?
If the answer to both is no, then, OK, I guess we just value transparently differently. If the answer is yes, you are more interested in your side winning then establishing good rules for governance.