I always thought it was because that was the way they built it for right hand drive (Japanese) models and never bothered to change it, but then someone showed me a picture of a Japanese car with the hand brake moved to the left - so they seem to do it on purpose. I sort of like it in my MR2 - it keeps it out of the way of the shifter.
The '85-87(?) MkI MR2 in the U.S. has the parking brake lever towards the driver's side. In a subsequent model year, the lever was moved toward the passenger. I suppose it's arbitrary, although the lever doesn't get too much in the way in my MR2. The new Celica's parking brake lever is toward the driver's side. Maybe the placement depends on its connection to the rear drum.