Why are people so rude?!

We just found out our baby's gender so I sent a text to all of our family inviting them over Saturday for a laidback reveal 'party.' Did not ask anyone to bring anything, acknowledged that it was last minute and made it clear that I understood if they could not make it. The thing is...that was Monday...and only ONE person has responded AT ALL. Strongly considering just cancelling it. Am I wrong in being upset that no one can take 5 seconds to say they cannot make it, though?!

ETA: I totally understand if people cannot make it because they have other things going on. That is not the problem. I realize it is last minute. My issue is that no one can take 2 seconds to say ANYTHING. Not yes, not no, not maybe, not I got the text and will get back to you...just totally ignoring the text for multiple days. And these are not acquaintances. Everyone we invited is our parent or sibling.