One reason is that MS negotiated a much more flexible licensing deal with the manufacturers (and paid a LOT of extra cash for the privilege). Others (as other posters have stated) are related to the graphical and physical effects modelling.
The licensing issues with the various manufacturers are incredibly tightly negotiated - and where Manuf A might be quite relaxed about their cars, Manuf B will not. From a game design perspective this is a nightmare and means you have to design to the most restrictive common denominator - or drop some cars. This happened in Forza 1 when a well known german manufacturer decided (at the very last minute) that they didn't want custom paint jobs on their cars... drop the decal feature or drop the cars? Sadly, the customizable cars went. The official (non paintable) race team versions remained.
#2234925, By korky Forza's Physics
korky 40 posts
Seen 4 years ago
Registered 9 years ago