reserves have nothing to do with taxes. The amount of reserves does not mean that this amount is annual profit.
Plus, avoiding paying taxes leads to serious fines + paying taxes with extra penalties. I see no reason for legitimate businesses to do that.
If it has nothing to do with taxes then those centralized exchanges shouldn't really worry about that aspect of sharing information about their reserves.
Actually, I agree that most legit businesses never avoid paying taxes, however they know most of the tricks to pay less taxes and still be safe from extra penalties.
If we look back in past then FTX is a good example for us, they never shared their proof of reserves publicly and users were still considering them as legitimate, but their collapse showed another side of the picture.