unless I'm wrong, it would be beneficial for the users to choose by themselves whether the site should have or not x question.
They do! Moderators are not the ones closing most of these questions. They are being closed by users with high rep, and flagged by users with less rep to indicate they should be closed.
The users closing these questions have exponentially more rep than is required to actually VOTE on the question. I'm not saying their opinion is more important, but it is.
As busy as they are, it's very unlikely moderators have extra time that they choose to spend by looking at old questions. They respond to flags mostly.
The ones which are low quality never get many upvotes anyway.
I'm not sure what data you are basing this on, but it's not relevant. Most of the "popular" older questions that are getting closed are getting closed because they are off topic. We had much looser standards of what was acceptable 3 years ago than we do now.
The only cons I can think of are... DB space?
...and the noise of a non-technical non-helpful question.
...and the bad precedent that confuses new users about what is OK on the site.
...and the noise of having all the high-vote questions be 3 year old poll-type questions which are no longer allowed.
Just because it's cool or popular doesn't mean it's appropriate, and that's the root of this issue. These questions are no longer appropriate for the site.
There's a thousand pages with funny lists and lists of programming books and other stuff.
There's really only one place to get extremely high signal-to-noise-ratio technical questions and answers, and as the site gets more popular we need to be more careful about sticking to that core value.
It's what makes the site uniquely successful, it's what makes very gifted people who excel in their fields continue to contribute here in such numbers, and it's why we all spend so much time here learning and teaching.