@Lox most likely because in modifying the lxdbr0 network’s raw.dnsmasq setting this would have caused LXD to remove and re-add its firewall rules, potentially changing the order of the rules in relation to another ruleset that is normally added after LXD has started.
See Lxd bridge doesn't work with IPv4 and UFW with nftables - #17 by tomp for a more thorough example.