People tend to mod as they´re bored, the new mod will only mask the boredom for so long until they look elsewhere!
In reality though, you get bored of any car eventually. Grass always seems greener on the other side..
totally agree with this, coupled up with an element of being competitive for some people, they just want to chase BHP numbers. The novelty will wear off anything eventually, it wears off a new car for me after about a week usually.