It's illegal to rent space to businesses you know to be conducting illegal activities. The mall operator can't rent space to a drug dealer or arms dealer, they can't rent a brothel, they can't rent space to human traffickers. Mall operators are not common carriers.

Read up on accessory laws in the US. Not saying it’s an open and shut case, but there is enough grey area that a DA wanting to make a name for themself for political gain could easily justify trying.

If they rented that space out to a brothel, would they be liable?