>>14932359>not understanding a gift economyEasy come easy go.
The point is to trade away things that are EASY FOR YOU TO GET, BUT HARD FOR OTHERS TO GET.
Late game mons, bred rare mons, safari zone mons, version exclusive mons, mons with good stats/natures/moves you bred trying to get something but have no use for, stuff with Pokerus, etc.
That's the point; it's low-cost to you, so if you DO get trash it's no big loss, but high gain to someone else, who hopefully appreciates it enough to do the same.
A perfectly-functioning wonder trade would be flooded with mons that are rare and amazing to everyone EXCEPT the guy sending them, who finds them perfectly pedestrian.
Legendaries and Shinies make no sense on Wonder Trade unless you're, say, restarting your game and want to make someone's day. Giving something WITH THE EXPECTATION OF HIGH RETURNS is stupid. It's like giving a priceless faberge egg to someone at the office Secret Santa and then getting upset when all you get is a Starbucks gift card.