It likely has to do with the print temps. PLA Silk fomilstions have additives that give it the metallic sheen that don't work well above a certain temperature; anyone who's tried to print PLA Silk above 200C could show you how well that works out. ABS can't print below 250c so that additive will be dead.
Also, vapor smoothing someone that has a certain surface appearance after printing will likely lose the surface appearance entirely.
Polymaker sells some "metallic ABS" that is not quite a silk appearance but appears shinier than typical ABS. I'd give them a try maybe.