Hi Garry... Welcome to G2G!
Those announcements are not so much to remind us to buy a gift for our aunt with the upcoming birthday (although they can serve that purpose!) as I think they are more to remind us of our ancestry and family history.
The more profiles you are connected to on WikiTree, the more names will appear on the birthday list when they apply. You can opt out of receiving such notifications by clicking the links provided with them, but you may find you enjoy getting them. I always get a kick out of being the only guy in my family to know when our great-great-grandmother's birthday was :)
It's always fun for me to run into a friend in town who I've done genealogy for and be able to say something like "Here we are complaining about the snow... while back in the 1700s your 5th great-grandfather, who was a Patriot in the Revolutionary War, was born this very same week." Amazing conversations have grown from just such interactions.
Thanks for posting your question here. Have a super day!