Because they can afford it (or are OK with racking up debt). It really is as simple as that. There are luxuries in life that will never be understood by others.
Some people don't blink about a $400 dinner for 2.
some people will spend $400,000 on a boat that gets used 5x a year.
etc...
Don't try to wrap your head around it.
Very true.
But a year after a $400,000 boat is released, the next model doesn't double in speed and functionality
It's going to be interesting seeing how Apple will market the Apple watch and what product niche(s) it falls into