Cruising (d)evolved from "Cops 'n' Robbers", which was originally some kind of pseudo city layout made from barriers on the autocross track, with some people playing police and other robbers that had to get away from them while navigating the barrier-city. Think NFS Hot Pursuit + city layout + superior driving physics + inferior crash physics. This was quite fun as it required skill from both police and robber to navigate the city fast without crashing and losing/not losing the other. This was sometimes accompanied by role playing traffic and innocent drivers and inventing different reasons for why someone was being chased by the police.
Then someone somewhere had the genius idea to remove the chases (read: fun) and call it cruising. Now you can pretend to make your daily mundane virtual drive to work, stand around a bit and earn virtual cash to buy/repair your virtual car. Sounds exciting, huh?