8 mil in the bank is a fukkin lot. That's liquid cash not cash plus assets. Imagine how much more he has tucked away in businesses, trusts and investments. Then on top of that add to the fact that he was never one of those 5 mil plus album sellers and then you'll realize that dude is actually pretty damn good with his money. I can almost guarantee most people you think are mega rich, don't have that kind of liquid cash that they access to. And I'm no Nas Stan.
Facts
Wealthy people engaged in actively managing their money keep the bare minimum of liquid cash in the bank.
Cash in the bank earns little to no return, and is
easily accessible via nuisance lawsuits, child support bullshyt (like Nas is currently going through), etc.
I'm willing to bet that Nas has upwards of $100 million invested across a broad array of asset classes in a variety of bankruptcy-remote vehicles, trusts, and other tax minimization / tax avoidance / liability avoidance vehicles.
What wealthy folks will do is have access to large revolving lines of credit collateralized by assets held in all of these vehicles should they need access to cash. A paternity lawsuit, car accident settlement, sex tape case, etc. can't access that line of credit to try and recoup whatever they're owed. It's a liability, not an asset

It also inflates the wealthy person's debt / income ratio should they want to go through bankruptcy proceedings to shed accumulated liabilities they are no longer interested in paying (see: 50 Cent).
A good rule of thumb is that most wealthy folks will maintain no more than 12 months' worth of expenses in cash & cash equivalents. Nas has overshot this amount by a pretty significant margin - I'm willing to bet that this lawsuit was filed in the midst of him rebalancing his investment portfolio and maybe simplyfing / rationalizing whatever trust structures he has in place to protect his wealth.
