My guess is because United moved to married segment logic for displaying PN/PZ/XN data that they simply removed it from the website completely now. Let's face it...those numbers were always zero because even though the international flight may have PZ space the domestic almost definitely did not. Hence it showed PZ=0. United likely got a lot of complaints about that because people would book elsewhere and/or book other flights and/or manually search every single flight manually (like most frequent flyers would do).

When I search MUC-SFO by itself PN/PZ display completely fine (albeit ZERO as expected - haha).

-RM