Except they hired the writer a year before Avengers came out. And what coattails? He had like 2 and a half seconds of screentime.
So what if the writer was hired before the movie came out, it's still being written. Add on the fact that the general audience showed excitement to Thanos' reveal despite the majority not knowing who he is, they just knew he was bad news; 2 and a half seconds or not of screentime, the point got across.
WB is showing heavy signs of desperation, with the failure of GL, the not as great reception to TDKR as TDK(it was still loved yes I know, but it wasn't at TDK levels as I'm sure WB wanted), the failure of the WW pilot, the half-ass attempt with CW'S
Arrow, the soon to be half-assed attempt with CW's Wonder Woman/"Iris", to the now rumors of the bull**** of JGL being Batman, and now Darkseid as a villain with no build up nor explanation of the character anywhere; yes I know it can be told in the JL movie, but then what happens to the stories of Superman, Batman, Wonder Woman, Green Lanter, and whoever else will be making up the League?(Martian Manhunter, Cyborg, Aquaman, Green Arrow, whoever, etc.)
It reeks of bad planning, bad writing and desperation due to lack of care for all properties involved.