Most copyright notices on these pages are invalid, so they would not serve as valid notice anyway, so your presumption is wrong (it also reminds me of the bear patrol episode from the simpsons)
First, the form is often wrong, which makes it the same as no notice.
Second, if the date is wrong, it depends.
If you use too early a date, you lose that many years of protection.
If you use a date 1 year or more after first publication, it's the same as no notice
So what you get by using wrong notices can be worse than nothing. You actually lose some protection.
As for the rest of the reason not to do it, because it's complete an total cargo cult lawyering that wastes tons of time?
You think you are getting something. You are getting worse than nothing. You are wasting time (this thread etc) figuring out how and when to update something, and whether it's legally correct, etc.
A copyright notice does indeed have utility, to the extent that it discourages people from thoughtlessly repurposing your content. Some folks, in the absence of a copyright notice, erroneously assume that the content in question is free for the taking.
The best protection is that which helps to keep at least some unauthorized copying from happening in the first place, not that which lets the copyright owner (expensively) go to court.
> You make the odd assumption it makes any difference to rates of copying. I actually would seriously doubt that it does.
Either way, including a copyright notice is an extremely-cheap hedge, with little or no appreciable downside risk; if it deters even one copier, it has justified its close-to-epsilon cost.
Except, as I pointed out, it has serious downside risk. If you do it wrong, you are heavily penalized by law.
If you do it right, you get some vague and possibly zero benefit.
> If you do it wrong, you are heavily penalized by law.
For U.S. works created after the Berne Convention went into effect in 1989, that won't be the case. Consider the possibilities under 17 U.S.C. 406(b):
1. If you use too-early a date in the copyright notice, you lose that many years of protection. If it's just a year or two, or even 10 years, that's almost literally rounding error compared to the term of copyright.
2. If you use a year that's one year too late (e.g., 2016 for a 2015-published work), you're fine.
3. If you use a date that's more than one year too late (e.g., 2018 for a 2015-published work), it's the same as publishing with no notice. But because it's a post-Berne work, you don't need a copyright notice. So you don't care.
So for post-Berne works, there seems to be almost literally zero downside to including a copyright notice of some kind. Even just the word "Copyright XYZ Inc." with no date would give you some deterrent effect, even if it turned out to have no legal significance. Am I missing something here?
First, the form is often wrong, which makes it the same as no notice.
Second, if the date is wrong, it depends.
If you use too early a date, you lose that many years of protection.
If you use a date 1 year or more after first publication, it's the same as no notice
So what you get by using wrong notices can be worse than nothing. You actually lose some protection.
As for the rest of the reason not to do it, because it's complete an total cargo cult lawyering that wastes tons of time? You think you are getting something. You are getting worse than nothing. You are wasting time (this thread etc) figuring out how and when to update something, and whether it's legally correct, etc.