Chris is referring to “moto” engines and not KZ’s because he’s referring to dirtbikes.
Please take your KZ comments to another thread.
However, to address your comment, KZ’s have dry clutches (except for Pavesi which are primarily used in road racing) so the gearbox doesn’t share fluid with the clutch like a moto engine. In a moto engine, the clutch during its operation wears away the friction plates, however slightly, and that further contaminates the oil. Due to this, the moto oil gets more contaminants vs a KZ thus my, and SwedeTech’s, recommendation to use a proper transmission oil in a moto engine (like Motul Transoil). Also, ATF is more slippery than transmission oils and will change the clutch activation.