I know there's been a huge debate on this already, but I cannot see why it wont be changed.
What is Stack's "off topic" meaning?
The term "off topic" is mostly used to describe and define "Types of questions Stack does not permit", or "not suitable" etc.
Those who feel it's clear enough, remember, something you have clear in your own mind that you understand perfectly, may likely not be clear at all to someone who has just discovered this 'something' and has no idea about it.
This is not necessarily about new users then, it's specifically about people who do not know that when stack refers to "off topic" it means "questions Stack does not permit".
That's a potential for a lot of people, and a great deal of new comers, because they would never guess this correlation from logic, experience of other sites (as it's unique to Stack), or even by eating unicorn dust on the errie first quarter of the lunar phase.
Here, only comments and answers could be deemed specifically as "off topic" as they're off topic to the question.
The fact the message then goes on to state:
Questions asking for code must demonstrate a minimal understanding of the problem being solved
Only confuses the issue even more as they continue to ponder: What is a topic? And now wonder: What has a topic got to do with my understanding of my problem?
I've seen this on questions where the reason "Too broad" would have been more suitable, but that's another issue altogether.
People not knowing Stack's definition of "off topic" probably think tags could be "topics", the question and subject could the topic as they define the topic. Not much else could be surmised as a "topic" for one to consider why it could be "off topic".
So the questioner asks a question, uses tags relevant to the question and the subject is a good summary of question and ties in the tags. They understand the problem they are asking about just fine. They believe it to be all good.
But no, because the issue was none of what they logically surmised it to be, as it's "not a question Stack allows".
Why should it be changed?
The fact these messages are to educate people and push them in the right direction, why use something quite vague to attempt to educate them?
Most other messages are pretty tight and describe the actual issue to even someone not familiar with Stack's specific ways.
Educate them so they can write a better question and contribute to the site - isn't this part of the aim?
You might as well just close it and have no message, in fact this would be better as it removes some confusion from the currently misleading message they get.
Potential negative outcome
So then they either:
1) Leave the site and not return;
2) Write another question, still not understanding the real issue so just as bad as the first;
3) Edit their question (as is suggested), still not understanding the real issue so don't improve it;
4) Come to Meta and ask what "off topic" means;
5) Lurk around and find out for themselves what "off topic" means;
Why they're bad outcomes:
1 obvious. 2 & 3 is a waste of their time, and likely other people's time who vote and potentially mods time, 4 same as 2 & 3 but additional people having to answer and post "dupe" links.
5 is only likely a waste of their time, but once they find out will join the group of "why is this saying off topic when it could instead say XYZ" and they become annoyed. They might even post on Meta suggesting a change, yet another thread about it...
Adding to 4 - They ask on Meta and yet again their question is closed. Even though the reasons to us/mods are clear why this would happen, from their perspective as a new user, getting their question closed that was asking why their other question was closed is not nice
Change it to what?
It's not all about one message, it's impossible to cater for all close/on hold scenarios with one message. It's about ensuring that every scenario is covered to provide people with a clear indication to the specific reason their question is closed or put on hold.
So used in conjunction with "too broad" and "Unclear what you're asking", as well as other comments, changing "off topic" to something more clear will stop all the confusion and frustration.
Just encapsulate the actual reason for the close/hold based on something that non-Stackies would understand, as seems to have happened fairly well with all other messages.
"Question is not suitable for this site". This is backed up by the current statement informing them that it can be re-opened if they can "edit the question to fit in with the rules" and a link to more info.
If they don't read the info from the link, well, you can't teach a dead monkey to fish...
Change makes people run for the hills
I understand the concern that introducing a new title may require having to educate people and bring confusion/more work/etc. However, it's quite simple.
Where you choose "off topic", put some new text to identify the change, such as:
o Off topic - will now show the message "Question is not suitable for this site"
Then whoever is selecting knows the old familiar off topic will now show a new message, and decide if the new message still fits in with their reasons for close.
And once after months it is familiar with everyone, drop the text "off topic".