it was an announced VATUSA sponsored event.
What was the VATUSA sponsored event? The Open Mic Night FNO? If that's the case, then you have misunderstood the Open Mic Night. OMN is an opportunity for all of VATUSA to staff up when they can. ZNY does not schedule anything for OMN but encourage controllers to connect. We had no-one prepared to staff PHL, but had people show up when they saw a ton of arrivals to PHL. Had it been the other way, you'd probably barely had a CTR controller if I'm honest.
I agree with everyone else in this thread though that if you have a problem with ZMA in this, a forum is not the place to take up your complaints about it. You reach out to ZMA, and if they don't respond to you, you email the VATUSA Events Coordinator.