Most leases have clauses stating something to the effect that tenants are responsible for keeping their units reasonably clean and sanitary. If tenants start complaining about roaches, a good landlord will do a bit of investigation and remind tenants of the importance of cleanliness, proper disposal of trash, etc.
a "good" landlord will lecture the tenant without solving the problem and a "bad" landlord will double the rent
At least in Oakland, it's the landlord's responsibility to manage pest control. It needs to be done at a building level, or else the roaches will just get shuffled around.