Deflocked v flocked is a hard thing to explain. Some people will place no value on a deflocked version as the pony is no longer original. Some people hate the fuzzy version and will happily pay for the time and effort put into making the pony deflocked. Its not that dissimilar to people paying for a custom in some ways - you pay for the artists work.
It also goes in waves. Sometimes deflocks are not popular, sometimes they are going through a wave that can make them very desirable and therefore price.
Its just a classic case of something being worth what someone is willing to pay; and what one person may pay may be nothing like what someone else is willing to sell out.