I’d guess it’s some variant of the bystander effect - in that it’s easy to assume that there are others in the community who are better placed to take an active role in these discussions, and so to leave it to them.
I think your description of “What will you discuss during the meeting?” is good, but perhaps people would feel more comfortable in making a decision to attend if there was more clarity on how the meeting would be conducted and what the desired outcomes were. e.g. is the intent to present current thinking and collect feedback? Go round the attendees to help brainstorm? Something else?
I’m speaking as someone who saw these announcements and thought it was fantastic that the Foundation is trying to get broader input - but also didn’t make time to join the meetings so far. I don’t know my thoughts are representative of others, or it’s just me!
Especially if there aren’t successful online meetings ahead of then, perhaps it makes sense to try this exercise at EuroLLVM in person?