I suspect that the company that is having its name/logo/image wants
control over how its name/logo/image is used and the way its seen.

For example, pretend GTP was widely released in its present form. the
Mazda is supposed to be poor on fuel mileage. Whether this is modded
into the GTP program or not is unknown (and doubtful). It's probably a
historical fact, not an indication of how the cars runs in the mod. The
mod gets rave reviews and thousands of ppl. are playing it via VROC.
Word of mouth spreads and everyone knows that when running a longer
race, don't use the Mazda, it gets lousy fuel economy. However, the
Mazda big wigs get wind of this and don't want ppl. thinking that all
Mazdas are bad on fuel mileage so they send the "legal beagles" after
RD.

Pure speculation, but I'll bet there's a little bit of truth in there
somewhere.