Here's what I think happened - he wants to bomb or invade or both, and was talking to the military folks, and somebody told him that there are a lot of flights in and around Venezuela - flights up and down the continent, flights in and out of Colombia (that cross over Venezulea), plus you have Aruba and the Antilles right off the coast with lots of tourist flights every single day from Europe and the Americas. There's probably a healthy amount of air traffic in that part of the world.
They probably told Trump they have to be careful about civilian flights if they start bombing or trying to move troops in and supporting them, and that if they issue a NOTAM Venezulea will be tipped off, and Trump being Trump, said "fuck it, you all are useless, I'll shut down their airspace and the surrounding areas and we won't have to worry about civilian aircraft" and then he goes on Truth Social and declares bankruptcy their airspace to be shut down.