why do people feel the need to buy expensive cable


I have tried expensive cables and one's moderately priced. I would say there were some differences but I can't actually say the expensive cables were better. IMHO I believe a lot of people buy expensive cables because they don't actual trust their ears and are afraid of making a mistake. They figure the expensive cables are better for the fact they cost more. If you have a difference of opinion or share the same thoughts, I would like to hear about it.
taters
 
mechans
Because sometimes it makes the music sound better. It's really not complicated. Not always BTW, sometimes.

shazam!
...because sometimes it makes a difference....

Exactly. If someone cannot hear a difference then they should not use anything more than stock wire in their setup and be happy with it.  For those situations where differences can be heard, those people should get the cables they like and be happy with them. 
Folks this cable stuff makes my head spin. Several independent skeptics have offered varied sums of money to cable companies to prove their products are better than off-the-shelf wire. Some of these offers have been out there for years. To date no cable company has accepted them. Why not? The publicity alone would be worth it.

And yes, the car analogy is valid. Whenever a publication tests cars they routinely publish specs and run every vehicle through the same tests (i.e. acceleration, braking, handling). Most other pieces of audio equipment (amps, speakers, etc.) include specs for various factors such as thd, etc. It is routine, for example, to include oscilloscope graphs, etc. with various types of equipment. I am sure you can think of other examples.

Can these be tweaked. Of course, as is true of the endless threads about amplifier output. BUT, there is still some objectivity. An amplifier cannot claim 200w output when it only has 20. At present, cables have NO objective measurements.

Until the audio industry agrees to some standards for measuring cables, they stand as only very expensive pieces of wire. If cable companies want to convince me to part with hundreds or thousands of dollars that could be spent elsewhere in my system they will have to do better. So I will add my own challenge to the cable industry, both those making and selling them: if your cables really are better prove it scientifically. If they can not I will continue to spend my money on improving other components that can be measured. If they can not they are living on borrowed time. Eventually this modern version of the tulip bulb bubble will burst.
A BIG +1 for oldguide.  Couldn't have said it better myself. 

I chuckle at anyone who would take someone's claim that such and such a cable "sounds better" as even minor evidence of a cable's ability to make an audio signal improve, or be less effected by negative outside influences, while on it's way to loudspeakers.