Why buy older digital gear?

I've seen a lot of Cal Audio gear for sale recently, most notably the Cal Delta and the Sigma dac. I recall these units where popular in the early 90's. Why spend $500-$600 on outdated technology? Is it because the selling price is much lower than the original retail price? I am certain that todays budget gear would surely outperform any of the older players? Am I wrong or are these components still worth a listen?
Thanks