First, I need to mention that the time period is determined by the views, not the age. Here's a quote from the meta:
Close votes age away harmlessly if the threshold is not reach after a
number of days. If the question has at least 100 views, close votes
will age away after 4 days; otherwise close votes will age away after
14 days. Each new close vote resets the timer, so all close votes must
be at least 4 or 14 days old respectively before aging occurs.
However, I agree with your latter argument. The reason could be that there is no notification for mods about closures, and they barely go through the closure review queue. If you take a look at the Closure Review History, you'll notice that only 5 of the last 100 reviews are done by a mod.
So it's somehow harder for these questions to receive enough close votes or a moderator's attention if they are not on the front page.
Having said that, I still find some good close votes on old questions in the queue, even though those posts are old, that doesn't mean they should be closed. We get a lot of low quality new answers on old off-topic questions every week.