The questions arrive one at a time, forever
You send a lovely picture of the invitation into the group chat, and within the hour the questions start. What time is it really? Where exactly is the hall? Do children come? Can I bring Ines? Each one lands as a separate message, and each one needs your reply. By the fifth re-typed address you are not hosting a party, you are running a help desk.
A picture cannot answer any of this back. It is a flat image: whatever was true the moment you exported it is what every guest sees, even after the plan moves. A digital invitation website is different. It is a page your guests open, and the page keeps the answers next to the invitation, so most of those messages never need to be sent.