Many accounts might be created by a single person for this purpose, which I think it is still not really worth it and I will explain. Anyone could create an unverified account like you said, but what is the essence of trading on different accounts when you will still eventually forget some of those accounts, and a user may eventually forget the password or details to the wallet where he has so many of those coins just because of some sort of discount.
No matter the amount of discount, you cannot trade a fund in more than one account at a goal,. And having to split those funds will be very stressful, and also to me, this is cheating which may eventually invited strict regulation on unverified account. Binance is already a big platform, so it would do them no harm if they start introducing KYC to the unverified accounts now.
I think the point is different. Right now many people still are using their account that they signed up with initially on Binance. But there is literally no point in keeping that account, you are better off to make a new account now since the 20% fee discount is permanent and might have a temporary nature. You will not trade from multiple accounts, you are
only trading from your new account.
No need to split the funds. And I actually contacted the customer service about this. It's a legal practice, the only thing they say is that you need to use a different document if you sign up for KYC again (e.g. drivers license instead of passport or the other way around).