Because it is based on Git, jj is not a CRDT, it seems to be a better merge algorithm (even though the details on their algorithms are scarce).

When I say "not a CRDT" I'm obviously talking about HEAD not being a CRDT, a Git repo is append-only, so the history of a Git repo actually is a CRDT (but that's not what the comment above meant).

I think the more important thing is that jj (and hg and git) don't use the AST at all, at least not yet. Does Pijul?