I quite often get the "we're not sure what we're doing that weekend so we'll let you know closer to the time". People seem to think "Maybe Attending" is an acceptable RSVP. Why can't they just tell me now? You're either free or you aren't. Don't wait for something better to come along and then text me the day before to say you're too busy to come! Grrr...
This is my pet hate, people who think it's ok to trade up for a better offer.

If they can't make a commitment to want to come to an event (and it's not a legitimate reason like someone being sick in hospital and they REALLY don't know if they'll be free)
then I'd think twice about whether u want them there.

I have a huge family and nonone RSVPs to anything - 10% reply rate if I'm lucky.

The only ones who reply are those who can't come, those who can assume we know automagically because they didn't say they couldn't.

We had 110 at our wedding and 80% of this were my family. I can count on my fingers how many rsvps we got, and very few people did not come.

I had to ring them all on the RSVP date.