What we have here (in the US) as a motivation for landlords to maintain and repair their rental properties is an overburdened civil court system. If a renter can prove that neglect by a landlord has been a direct cause of illness in the tenant or the tenants children, due to mold or simply drafty and damp conditions, that landlord will be in a financial mess for a very long time to come.
Landlords often find that it's easier (and cheaper) to just spend the money on maintenance and occasional improvements rather than deal with a huge, court imposed judgement.
Also, in California, if a landlord fails to comply with health and building codes after several requests (in writing), there is a method that a tenant may use to withhold payment of rent until said repairs are made. And then, the tenant cannot be evicted on the grounds that they reported the violation.
It looks good on paper anyway...
