You only have to go as far as "Problem" to see bans on general words or phrases do not work.
And this is just the variations I felt like trying. There are problem hundreds more different variations caused by the same
porblem problem. Plus, who knows how many hundreds (or thousands) of these workarounds have already been edited out by other users.
This shows that rather than actually improving anything when they encounter the blacklist, people will just work around it. And you end up with a lot of ugly workarounds that are probably as bad or worse than the original rule you tried to enforce.
Then you have to deal with the false positives. Can there be a questions where it is entirely appropriate to not to have a question mark? Absolutely! And I am virtually certain I can come up with an excellent question that contains either "it's not working" or "it doesn't work".
And let's not forget that there are still 46,802 questions with problem still in the title. These questions cannot be edited unless someone changes the title to remove problem. Adding new banned phrases or keywords would make another obstacle to people who want to edit the post as they now will need to figure out how to rephrase the question.
The point is banning those words or enforcing a question mark may seem like it will help with question quality, all it will do is annoy users who plan on using those phrases appropriately while at the same time most of the people you are targeting won't actually fit it, they will just work around it.
(The counts above don't quite add up as some of them above are duplicated in a couple of different searches, but I still think it gets the point across).