PKD

A friend recently informed me about the SF author Philip K Dick, so I ran a search through blogger to find out more about him. His works to name a few include "Minority Report", "Blade Runner","Paycheck", and "Total Recall." He is described as writing some of the best SF during the 50's, but his work not recieve much admiration until decades later. My question of concern is why did the critics during the 50's not credit PKD with the recognition he apparently deserved? How has the standard of worthy SF changed over the past 50 years???