You don’t have to send that reminder email the day of the thing you planned. People replied two weeks ago. Surely it’s on their calendars. It’s definitely on yours. No, you don’t need to send a reminder.
But you could. And if you did, somebody whose day got away from them and forgot all about it might be enabled to participate, and maybe the thing you planned is just the thing he needs on this particular day.
So no, you don’t need to send a reminder. You’re working with grown ups. You’re not required.
But you are able. You are allowed to be generous and to extend a small gesture of repeated invitation, just the kind of small gesture that could make a world of difference.