I've seen this arrangement in starter motors for cars. The main advantage is probably ease of assembly. If you've ever taken apart the back flange of a small DC motor and tried to put it back together you probably know how finicky it can be to push both brushes outwards while trying to push them over the commutator.
Even more finicky on a starter motor, there are
four brushes to wrangle simultanously.
P.S. It's surprising how little of the winding space is being used in the rotor, normally the passages are packed. Presumably they're getting away with finer gauge wire for intermittent use - maybe they've actually used de-rated starter motor hardware.