[I'm not a Google employee, but I am a Ph.D. student who has gone through the academic publishing process a few times ...]

Publishing in academic conferences is not the only way to be "non-secret", nor is it the fastest way to get early feedback on usability and systems design issues. In fact, it's a pretty slow way to get feedback. The sorts of conferences that Googlers submit papers to have an acceptance rate of 10% to 25%, which means that most papers get rejected; moreover, it takes a ton of effort to write up and present a paper to an academic audience using writing conventions that are very different than those required to write engineering design documents. Given those low rates of publication "success", it's not surprising that Googlers put their efforts elsewhere.