The only reason that I can think of as to why CZ still clings to the polycoat finish is,
A. It's cheap.
B. On the steel framed pistols, as we all know these are cast, from time to time, small imperfections show up on the castings, small pits, inclusions, are probably more common that we know, anyway polycoat being a thick coating can be used to cover up some of these smaller flaws in the castings..I myself have a 99021 that I had the frame, barrel, slide, saftey levers, and slide stop black nitrided..When the polycoat was removed from the frame there were two very small pits just above the rail on the right hand side of the frame. I guess that CZ felt that these were cosmetic (which I agree with) and simply sprayed the polycoat on it, and covered them up.
If CZ wanted to go to another coating or process, then they'll need to be much more critical of what passes and what dose'nt. Or, they could spend a bunch of money and start forging the steel frames, and get rid of the problems entirely..