Why is shiny Riolu impossible?

I’ve done successful dexnav chain hunts with a few Pokémon now. Search levels at 255, chain is at 100 (as you can see above), and yet with Riolu, I’ve been reloading my save state nonstop since yesterday with zero shinies.

I know Riolu has a much smaller encounter rate in this area, but does that impact the 2% shiny chance for it as well?