Because I often don't know the range I'm looking for, it could have been yesterday or it could have been 4 years ago. If I select last 12 months I might miss something 13 months ago. There's a lot of ambiguity in what I'm searching for (otherwise it wouldn't be called a lookup) and when I'm looking for current information then weighting by age is a lot more natural.

Another issue is that I don't know what the filter is selecting either, a 6 year old article might be better if it's been updated, but I can't tell from the interface what property is being filtered.

I often happen to search for things in multiple intervals. Often the top results are obsolete, since they are more than a year old.

What drove me nut's, is that their QA didn't catch the bug with the date format order for years. It only recently got fixed. The calendar selection was regional and put in the date in the regions format (Often dd/mm/yyyy), while the query form expects mm/dd/yyyy.