Yeah, the thing with ISO kits is that they generally don't tip. People hue and cry over the lack of them, but then when they're there they either complain it doesn't have their specific regional variant and don't buy it, or that if it includes it, it's too expensive, and don't buy it.
For a non-PMK example, the uproar over the Triumph Adler set's ISO support. It covered an ISO board, but people weren't happy with which keys it had. (A minimum, to avoid making the set too expensive for everyone.) More complaining was done over the lack of, say, Italian or Norwegian keys than happiness that it'd actually cover a board. If it HAD had all the various ISO keys, nobody would have bought it because it would have been hideously expensive. (Look at the Granite regional pack. It's huge. It didn't sell enough at any point to meet GMK MOQ either.)
Basically, ISO is impossible to support feasibly with the demands people make of that support. It's not just the ISO enter and the 1.25u shift key and two extra 1u keys. Since the areas where these sets are located are so relatively small, and custom key sets are a niche corner of a niche hobby...
tl;dr ISO 'standard' isn't very standard and support is a difficult prospect and people only want their own local keys but there aren't enough usually for any one region to actually do this.
