Hi
The GNS530 comes with an older NAV database, and in that version airports with runways shorter than 4000 feet is not implemented. That is for the WORLDWIDE.BIN file who contains the entire world. If you van get hand of a new databasefile, that contains onlye a region that you fly in, example, USA, Europe etc, then alle airport in that region is implemented.
The reason Jeppesen did not include "all" airports, is that the file got bigger than the Real Garmin GNS 530 could take.