Because the track is much larger. More frame work, more textures, more detail, it's so much bigger then any other track so larger draw distances etc. Think of it like a battlefield map compared to a cod map.

As I said, I've played loads of free to play games without spending a penny. There is no catch. Peer pressure is not a fault of the games*developers.
Some people gladly pay for items in the game, but you are not forced to.