@norainhere I think it's because Patch X Remi doesn't have any of the power dynamic of Sakuya X Remi or Koa X Patch, or the inherent weirdness of Flandre X Remi. Reimu X Remi comes close, but since Reimu gets shipped with literally everyone, it loses a lot of the impact as just another brick in the massive foundation of Marisa and/or Reimu works. It's a pairing that makes sense, isn't overdone, and seems for the most part grounded in mutual respect, not physical attraction. (Most of the time.)
I still wish we saw more Reisen X Youmu, though.