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Well, you couldn't be arsed to invited everybody personally so the recipients of that invite couldn't be arsed to reply to you personally.
I totally get where you're coming from but surely you've seen this pattern before WhatsApp was a thing? Have you ever tried to organise an office Christmas party with a group email and ended up having to visit everybody's deals individually to get the answers?
The counter argument to this is that you tend to get personal responses if you invite people personally and lazy/no responses if you can't be arsed and just send a group message.
Invite people casually, expect a casual response.