>>281420550
It's a mix of OP using Judas, who compresses the shit out of every anime, and the ZnT BD only having upscales for S1-3.
Upscaling a lot of SD era digital stuff like ZnT will tend to give it a muddy look. If you want a particularly bad example of this, the old Digimon Adventure BDs were a travesty of colours not looking right, lots of blurry edges. A lot of companies just didn't preserve the resources to render the anime out again in HD I guess- the only one that did seems to have been Detective Conan, which has the best SD era remasters of a digital anime I've seen.