Ah, because it hides the tires and makes the car look abandoned along with depending on the sunlight will create grassy reflections & odd shadows. "A car guy that shoots for GM high performance magazine said never put a car on a surface it wouldn't ordinarily be found (i.e. cars on grass). Seems logical to me, even though the shot may look good. It's just unnatural." If you had a 4x4 or truck, then grass would suit it imo.
But since its an Alero, maybe a parking lot, some nice new black tarmac.. or even by some funky looking old building, over a bridge, etc. It just makes it more visually appealing. You could also try getting down on your stomach and taking some really low pics looking up.. makes most cars look more aggressive (and dont forget to turn the wheels all the way for a couple shots..gives an illusion of moving or a "ready to rock" look)
And try to always shoot on the side where the sun is shining. Move the car so the other side is showing against the sun if you want a certain angle dont just walk to the other side of the car
I like photography lol.