On Stack Overflow this was actually a pretty big deal. Very early on, while the Stack Exchange model was still developing, things were pretty wide open. The community was smaller and the occasional joke or mildly off topic question was tolerated because while the site was small the problem was small.
Then the site grew...
What was once the occasional errant post became a daily annoyance, so things changed incrementally to prevent some of the flood of annoying nonsense.
Later down the line, there was a flood of noise on Meta.
"Why can't I post X, high rep user Y posted it and got 100 upvotes, this is obviously discrimination against new users!"
Obviously this was also annoying. The old, highly upvoted question didn't fit the current site standards, and it didn't have anything to do with the rep of the user posting it, but there was also the perception problem to deal with.
Eventually the Historical Lock was developed to handle some of these questions. While some were just flatly closed and or deleted, the questions that the community was particularly attached to could be preserved with a disclaimer:
locked by Moderator♦ Mar 16 at 20:01
This question exists because it has
historical significance, but it is not considered a good, on-topic
question for this site, so please do not use it as evidence that you
can ask similar questions here. This question and its answers are
frozen and cannot be changed. More info: FAQ.
Long story short...
This is a normal developmental stage for a Stack Exchange site. As we develop what is and isn't a good fit we'll occasionally need to go back and close or lock some of our earlier posts. But don't worry, it's a good thing in the long run.
For more info see:
What is a historical lock, and what is it used for?
Should I vote to close old questions?