Where exactly did you see the FPGA sale? It could be some older miner using them and are not selling off the hardware to someone else at a price because its is comparatively useless now.

ASICs are the way to go with any type of mining. I still cant remember of any altcoin that would be profitably mined with FPGA let alone worth recovering the cost of acquiring them and setting up the place, electricity and maintenance.

But I agree with @badbart that future altcoins may have something good for FGPAs running their algo but then again there would be the problem with newer hardware coming up to compete compared to older one being sold.