I think you just answered your own question.
I'm sure there are psychologists out there who can better answer the question of why people tend to keep wanting bigger things. Well, okay, that's not entirely accurate as I'm the opposite — I tend to like things smaller (eg. smaller laptop, smaller cellphones, etc). We all gravitate towards what we think of as better, though, and for most people that means bigger. Don't ask me why — I'm no psychologist — but that's just human nature.