Total guess, but maybe they see the actual usage numbers of developers that use Go? AND that number is not very high. Also, how well does Go translate into Android apps? Just a guess.
I'll keep writing Java to build Android apps though. I'm sure it's "more fun" or whatever, but Java's worked just fine for me thus far. I'm used to the verbosity, and have no desire to start from scratch with another language. If some huge benefits were presented, I would. But, I'm failing to see any.