If a landlord does not live up to his obligations, what choices does the renter have? He may move out, most commonly with the option of either breaking his lease, forfeiting the deposit, or wait for his lease to run out, paying for services that are not satisfactory. In other words, the landlord has no immediate incentive to fulfill his obligations satisfactorily, at worst he can receive bad word of mouth. If the renter does not fulfill his obligations, i.e. stops paying rent, the landlord can have him evicted for free by the police.
If the police were not here to fulfill this role, the landlord would have to pay a security force to play this function. This would increase the cost of doing business, and all landlords would have to charge higher rents. Cooperative housing would thus be more efficient, and be able to compete successfully against, traditional landlord/renter housing, not having this additional cost.
In other words, traditional landlord/renter relationships are a byproduct of The State.