Landlords typically don't accept cash for a variety of reasons. One is fraud but the other main issue is security for holding/transferring that cash and fact they have predictable schedules they'd have cash on hand.
I estimate the building I'm renting from right now would have anywhere between $650-750k or more revenue per month, most of which probably arrives in a one week or less window. That makes them a target for all sorts of potential thefts: employees, residents, burglars.
I've rented at many places and I've never once encountered a landlord that accepted or wanted to accept cash over secure electronic transfer methods, even for minor expenses like a consumer credit report check.