That's the generic label on the post, the real reason is usually it's "off topic".
The bigger problem is that moderators close questions that re ask 5 year old questions, irrespective of how much programming has changed. They built mechanisms to deal with this but the karma limits to use them are so high that no new user can so stack exchange are now suffering from the same kind of reverse feedback mechanism Wikipedia has.
New user arrives, asks simple question/fixes a typo, mods shut question down as dupe/bot reverts edit, user comments saying old question isn't accurate anymore because language X has change in way Y and he wants an answer for how it works in language X now/user fixes it again, mods don't care having moved on to other posts/bot reverts it again, user leaves in disgust.
It's unfortunate and very difficult, but it's worse for stack exchange because they want the selective pressure against "bad" questions but the community are currently suffocating the churn required to keep the questions relevant to current.
The bigger problem is that moderators close questions that re ask 5 year old questions, irrespective of how much programming has changed. They built mechanisms to deal with this but the karma limits to use them are so high that no new user can so stack exchange are now suffering from the same kind of reverse feedback mechanism Wikipedia has.
New user arrives, asks simple question/fixes a typo, mods shut question down as dupe/bot reverts edit, user comments saying old question isn't accurate anymore because language X has change in way Y and he wants an answer for how it works in language X now/user fixes it again, mods don't care having moved on to other posts/bot reverts it again, user leaves in disgust.
It's unfortunate and very difficult, but it's worse for stack exchange because they want the selective pressure against "bad" questions but the community are currently suffocating the churn required to keep the questions relevant to current.