15 years ago today, Satoshi Nakamoto and Martti Malmi entered the word BITCOIN into the annals of world history through the registration of the domain name BITCOIN.ORG.
I don't think that anyone still cares a lot about the anniversary of that site and that's why no one is celebrating its anniversary. Like @Poker Player said that the forum is bitcointalk.org not bitcoin.org and that's a valid reason for the members of the forum to not celebrate 15 years anniversary of that site. I also believe that the site is very important in we go back in the early days of Bitcoin, but now a days no one is that much interested in celebrating its anniversary. I hope you got your answer and if you are satisfied with your answer then kindly lock this thread.
I do not think that might be the case as I feel the community is more into celebrating the reason why Bitcoin become famous. Another reason I believe that most community members are active on the forum than the website. Though Bitcoin.org is the only website where you can read the whitepaper in different languages which according to me is a big achievement.