Speaking only of the US, some people would rather just say yes to someone to be nice in that moment, and then not show up to the engagement. Some people feel that it is more rude to say no to someone in person. I do not agree with this, but some other people do. It is hard for them to say no to someone. Instead of asking as many people as possible, it may be better to ask people who are interested in the event personally or you have a good relationship with. These people would be more likely to attend then others who do not have a vested interest. I hope this helps!