Everything with Joker's name on it sells well. Tons of popular but widely considered bad art sells well. LIEFELD continues to sell well.
Selling well is not necessarily a sign of quality.
We don't hate everything, I personally love a great many things, but the writing in Three Jokers is fucking appalling. And that epilogue ending (the piss icing on a shit cake) was a direct slap in the face of Alan Moore and anyone who has ever enjoyed the Killing Joke.