There are many kinds of big topics, implementing such a rule might not make sense. Not all large topics are spam.
For example, in the Portuguese tab there is a topic dedicated to books, and another dedicated to movies. These are topics that over time have become big, but it's not spam, because it talks about several books and movies. Let's say it's a mini book or movie club.
I believe that icopress, when giving this alert, is because it must have in mind some topic or some users in specific.
This is true. We have similar topics in the Croatian board. We have topics for certain blockchains (like Ethereum, Solana...) and all stuff that matters oke of that topics is being discussed in those large threads. That doesn't mean it's spam.