Because of point 1i of the code of conduct of this forum. Necro-posting isn’t really welcome in the majority of forums on the internet.
In rare cases a necro-post may be justified when actual new information is added. However in most cases the poster usually violates point “1g” of the code of conduct as they try to hijack the thread.
ps: @MelvMay I noticed the code of conduct still has a link to Unity Answers at the very bottom. I think it’s time to replace that link.