Don't most "serious" companies have lawyers that will spit venom at you if you even think about looking at code that doesn't have a permissible enough license?
implementing controls to prevent or detect this kind of copypasta is very hard.. even more so at larger "serious" companies that have dozens of development teams spread across the world working on an enormous catalog of products
this happens far more than people want to admit.. there's a very slippery slope when it comes to searching for help online.. it's amazing how quickly a google search leads to a stackoverflow post that has sample/example code which then winds up in your company's codebase.. even at "serious" places
writing a clear external code usage policy that's covered in those yearly training programs that developers hate and blow through as fast as possible is about as good you're going to get stopping this kind of thing
The controls to prevent developers from doing this sort of stuff in a serious company should be to let them know they will face disciplinary action/lose their job if they pull it.
They are rarely used.
Doing WTF you want is still limited by copyright law. You could argue that WTFPL is also an implied copyright reassignment, but I would not bet on it.
CC0 tries to mimic this but here the tricky part of permissions comes into place. If I give you permission to do anything and you remove the permission text and claim the work as your own, do you still have permission? It a rather popular discussion in regard to cc0, and the consensus where I have seen it seems to be that you need the license in order to have permission. I have also seen lawyers arguing that copyright law itself has limits on what rights a license can give, such as attribution.