Wonder Trade is great for collecting foreign Dex entries. I only need a Korean and a French Pikachu to have all of them.
They trade them because they want to get cool Pokémon with little effort. I used to do that until I got that speech Lyssandre gives you after the 5th Gym. I. Fucking. Cried. Since then I only trade breeding spitbacks and Vivlions I get from random Scatterbugs. People should release more of those common Pokémon and less of the others.Best thing I got through Wonder Trade was a Ho-Oh.
Not great IVs or anything but it did give me it for my Pokedex.
I don't understand why you constantly see like level 3 Weedles and Pokemon that are obviously catch very early game with no value what so ever really. Are this many people starting a new game and just trading them or are people just trolling? Personally, I take those 'mons I know no one wants out. I release them from the harsh life of wonder trading.