Every time I organise a lunch or dinner, be it for work or friends, it seems impossible to get a definite yes or no out of some people. I've suggested a lunch for later this week as I'm visiting a town some way from where I live (I do this every couple months) and thought it would be a good chance to catch up and get out of the house after Christmas. The usual four or five reliables immediately said yes, but two said 'I hope I can make it' and two have not replied at all (but have commented on the WhatsApp group the invite went out on). I have directly asked them for a commitment or answer either way.
I also get people dropping out last minute for the most spurious reasons. Last year we had an embarrassing time when 8 of us booked dinner but only three actually made it - the restaurant was not pleased.
I feel if you get invited you say yes thank you or sorry can't make it, if you commit then you turn up unless you've broken a leg or something! And please don't say 'I hope I can make it' and not answer one way or the other at all!