Companies trademark things all the time to protect them from people who would destroy a brand. If anything Jack is the kind of guy to take one for the team and trademark GIS Day so anyone can use it to promote GIS without fear that it will be used by porn sites (think about it). Sure Esri promotes their software in their presentations, but that’s what we all do on that day. The core concepts work anywhere so don’t get stuck in the weeds.
GIS Day is nothing to be afraid of. Plus Jack was hipster well before you were born.