The idea of the quote button remaining active is to be able to copy quotes from any post at any time.
I had the idea that information would emerge that the topic was closed. But it seems that there is no such message after all.
Probably not just to copy the quote as I think but also to reveal the raw link if the thread contains some source links and edited on the URL.
Active quote button is most likely being used to copy the post in a thread that is locked. I also done the same where I am quoting the post and share it to where I am joining in discussions. If I haven't see the color difference between the quote then I wouldn't have known that it has different colors when it is locked and open topics. What you explained is also what people do to check if there are urls or not but as I have said, it is mostly for quoting posts for reference to different topics through using quote.
