Initially, Rat had 3 individual seats with dividers in between, but shortly after opening they removed the dividers and made it a front bench and a back bench.
I’m not sure if they ever get up to 4 people (1 adult and 4 children for example) in the back, but they no longer have the capacity for single rider given it’s a bench with undefined seating (like MMRR).
Alternatively, (and likely the more likely driver) too many Americans couldn’t fit between the dividers, causing delays and decreased guest satisfaction that exceeded any potential benefits from single-rider.