"why do people feel the need to buy expensive cable"
I'd be surprised if anyone chooses to buy expensive cable, but that depends on what you consider expensive. My definition of expensive is an amount higher than I can, or am willing to spend. I try not to buy expensive anything. By my definition, everyone has a different bar height for expensive. Many Mercedes owners won't consider buying those expensive Bentleys.
Few of us start out buying gear at the limit of our spending tolerance. We learn as we go, taking incremental steps until we're satisfied or at least hit our spending limits. For me, I'm now done with my entire setup including cables. Could it be better? You bet. Every component I have could be improved, but sonically better gear is too expensive.