It’s because it’s non-trivial and is going to take some time to implement and optimize it in relays. I wanted to take a stab at it in nostrdb. It will use a few more lookups for sure, but lmdb is crazy fast so i didn’t think it would be a huge issue. Our roadmap is planned for a few quarters in advance and delegation is not even on it, people are busy with lots of different issues. The idea that it’s not implemented immediately therefore is bad is crazy to me.