Blizzard didn't forget about it though, they just ignored it until it became too big to ignore with Elysium, and then took it seriously and launched a great version of vanilla WoW with Classic.
They very famously did not ignore it, with the whole "you think you want that but you don't", the shutdown of Nostalrius and so on. People were going to jail for WoW private servers before 2010
Citation needed on jail time for WoW private servers.
Source: I made it up, apparently, my memory failed me and they never went to prison. They just owed Blizzard $88594539.
yes, I meant ignoring the customer base that wanted it, but actively denying them is probably a better term. pserver shutdowns always will happen regardless if they're visible. I used to do a lot with them when I was young