How is it poor marketing?
First, it's not being advertised as being in it, I just hypothesised they could do it to begin the hype dragon. Just the date, not them telling people to watch to get the reveal date, just for it to be there unexpected and mysterious to start the hype, then they can do what you seem to want and put it on social media.
You're also acting like the contents of Nintendo Directs don't get spread out to social media and news outlets.
Your argument against this is illogical and flawed.