Search function is not working properly. You can try using Google search and put site:bitcointalk.org after whatever you try to search.
If you could see my face you'd probably ask if I was rolling my eyes and laughing at you, but I'm not. It's just so awful that one has to do what you described in order to search the forum--and I know damn well what you say is true; the search function is and has been broken for a long time now.
This does not happen only in the forum. I have repeatedly encountered sites that have an internal search engine that searches worse than google. And I guess not all of them are broken. In the end I go directly to google every time. It is worth considering whether it is worth having an internal search engine, although I guess that in this forum it makes much more sense to have one of its own.