Some examples of answers to your question(s):
#1 Recession- people strugglin to make ends meet or unemployed
#2 Saving up for the Concords, Columbias
I'm one of them
#3 Complaints about the most talked about word "QUALITY"
#4 Nike releasing new lines of footwear
#5 Not every shoe do people consider them as their Grails or worthy of buying
#6 Resellers!!! Their jacked up prices are
#7 Bargain shoppers- looking for a better deal, not willing to drop $150+ on a pair of shoes
#8 Some people are just too cheap or tightwods
#9 Retiring from collecting or retiring from, as some say, "The Shoe Game"
#10 Failed releases-ugly colorways,materials, etc.
#11 Fakes flooding the market- fakes are now looking closer to the Authentics. Some retailers have sold fakes, mostly the Mom and Pop stores
etc... too many to keep listing but the top 11 main reasons.