It's pretty random what search results you get on the GTS.
Consider the sales for D/P/Pt,
and then imagine every trainer putting up at least 1 pkmn for trade,
divide by 493 total pkmn,
and its a lot per pkmn
but thats just an average
if its a good/starter/rare pkmn you're trying to trade then the no up for trade is prob higher on the GTS,
with hackers putting up more than there rightly should be.

Sorry but i don't think there's any help for this.