Fialex aims to give exposure to highly rated items with low sale numbers in Theme and Code markets.
When you have low number of sales, getting exposure to your themes or plugins in markets is very difficult. Once the initial exposure when you first list your item expires, you rarely can get exposure to your items.
This is valid especially in big markets like Themeforest, where there are established, long standing themes, plugins with huge number of sales.
Fialex lists these low sale, but high rating items, therefore giving them exposure that they could not get, along with its own listings.