And really, as they're adults I don't get a say?
They had the first two jabs as soon as they were able with no objections at all.
They're not saying they won't have the boosters, more that it's not convenient to have them now. They don't want to risk a couple of days' illness in the run up to Christmas and having to miss events (which of course they will have to if they test positive anyway).
All the way through they've followed all restrictions and tested regularly, now they feel they're going to make the most of being allowed to do things while they can.
It's hard to argue when the risk to them personally must be minute, but...