There is no point of having insurance fund on the same site. Consider for a moment, if the site is completely hacked, the funds on the site and the insurance funds both are lost. (although chances are less of hack with binance)
The Secure Asset Fund for Users by Binance or commonly called SAFU is not really stored along with the rest of the exchange funds. Accordingly, it is being kept in a cold storage separate from the site's fund. So, I guess a successful hack on the site does not mean the insurance fund is also compromised. That's highly unlikely. CZ must have known better than storing the site's fund along with the insurance.