why do people feel the need to buy expensive cable

Interesting discussion. 
I think cables absolutely have a strong effect on a system.
As a general statement, those who have moved up the ladder over time into reference gear generally swear by spending a fair amount of proper cables. My advice to anyone is try a handful of quality cables at multiple price points before settling into a decision. Spending $80k on your system components and connecting them with $1k in cables is false economy and you will never hear the systems true ability. For clarity, this does not mean one must then spend $30k on cabling to do justice either. 

+1 with agreement with referenceaudiomn.

I meant will not guarantee great sound but opens up more options.sorry for typo

Spending crazy money on cables is not the answer.  There has to be balance. Better equipment has to usually be fed better cables. I went up the chain in high fidelity and they do get better going up the chain.  There no way I would spend more on cables than actual equipment. I have a challenging room that affects my sound as well.  Hardwood floors, odd shape and reflections. I also can only put my speakers so far apart. 

Everything matters... That said, I believe a lot of folks get caught up in the PR (b*llsh*t) techno-speak or theory, and often the bling. Yet, good sounding cabling inescapably, has research, materials, and labor associated with its cost.

In any highly resolving system and most situations, I find the choices of good cabling to be a critical part of the HiFi puzzle. 

To what Tonykay just queried, Yes really. Yes, seriously. Melbguy1 is sooo spot on!