As it was mentioned here, the main reason is that we cannot put on "coming soon" titles which are not 200% ready to be released. And you don't know guys in such a crazy mode we work quite often on our releases;) Sometimes we get approval (or not;) hours before the planned release, and to the very last moment we keep something as an option B. I wonder if someday we will have so bad luck due to different reasons that there won't be nothing to release on certain day. Looking on number of weeks and just pure probality it has to happen some day. Especially that we expect that more of the biggest publishers will join GOG, and they usually work sooooo sloooowwww...;) (and have soooo weeeeird requests....)
Other reason is that sometimes we would like to make smaller or bigger surprise;)

yeah, yeah... just a last look, what is going on;)