If you are familiar with the late 90s GPs you'd know they look absolutely absurd with no spoiler on the back. Like I said, it happens. People try to save a few cents on weirder things. Or they just hated the look.
Either way, there was an option to not have something that cost next to nothing it is my point.
When I had my Grand Prix GT there was an option to delete the rear spoiler, it took something like $15 off the price. And people selected that option more than once as I've seen the cars without them and there were no holes for it either.