Is letting me into your house to read a book on your shelf or a newpaper a security risk? It's just static content on a page you say. Well, this is nasdaq.com. Even their blog site is a source of security concern both as access to a domain that hosts a lot of critical content and even static stuff on nasdaq matters.
Imagine a bogus post ending up on their blog that crap cryptocoins have been approved by regulators for direct trading / custody and some random ETF has gotten approval for a direct coin ETF offering etc.
The cost/benefit of dealing with tor on your network for a place like Nasdaq is not even close - NO BENEFIT to allowing it. Literally no one they care about (ie, folks paying them big bucks) will complain if it is blocked. So it's blocked. Simple.