I was pondering why the lack of high octane on the route, and think the reason 93 Octane doesn’t exist on the route is probably due to the altitude of I-80 above sea level.
I-80 varies from 4,000 to 7,000 feet, so at 4,000 feet 93 octane converts to an equivalent octane of 91, and at 7,000 it’s 89.5.