Jeet Heer wrote an incredibly well constructed essay on breaking the Hugo Awards, Sad Puppies, Rabid Puppies and the fallout, on website New Republic. The core issue:
“Between 1959 and 2014, the fiction nominations went to women 22 percent of the time… the percentage of female fiction nominees has shot up, reaching roughly parity levels between 2011 and 2013… This year, in reversion to historical norms, men make up more than 80 percent of fiction nominees. The Hugo gender backlash is a direct result of a conservative coalition that came together in 2013 under the satirical rubric Sad Puppies.”
Who, what, how and why. The entire essay is well worth a read.