These are two reason we don't have Thanks for anonymous editors:
1. Anonymous editors don't get notifications
2. Multiple editors often share the same IP address
Problem #2 isn't as prominent as it use to be, but there are still many
large companies and schools that connect to the internet through a single
IP. I imagine that once IPv6 is widely in use, this problem will go away
and we'll be able to turn on all notifications (including Thanks) for
anonymous editors.
Ryan Kaldari