Problem is that most people like to buy cheap, so manufacturers balance between acceptable quality and saving few cents.
I admit it right away: I like to save money because I feel I don't have tons of it hidden under my pillow and find other meaningful uses than buying tech stuff. But: I don't want to buy "cheap" either, because it indeed means buying double. Alas, the solution "just get a 1dx+600L+whatnot" doesn't help either.
The problem here are the reviews: For one reason or another, there's a strong pro-manufacturer bias on Internet sites, not to mention yt amateur unboxing. You really have to resort to forums like CR to find users calling Yn trash what it is. And even then, you have to clear the fog of "isolated qc problems" and "just get it replaced under warranty" to see where systematic, not statistical problems are.
If there'd be more matter-of-fact reviews, 3rd party manufacturers like Yn would probably lift their prices a bit, but stop saving cents where it hurts. Lens manufacturers like Sigma and Tamron lead the way - they don't do "cheap" anymore, but "value".
Let's hope this Yn 50/1.8 is at least on par with Canon's original not only in the specs and "first impressions", but on the long run - but then again, in this special case it isn't difficult to do :->