Why a clean home can still get roaches
You can have cockroaches even in a spotless apartment, because in multi-unit buildings roaches often spread through shared walls, pipes, and vents from other units or common areas — not because of anything you did wrong.
Cockroaches travel through the tiny gaps around plumbing and electrical lines and move easily from one apartment to the next. A clean unit next door to an infested one can still get them. They are drawn to warmth, moisture, and any food source, but keeping a tidy home does not make you immune when the building itself has a problem.
This is exactly why building-wide infestations are usually the landlord's responsibility to treat, not the individual tenant's fault. If a landlord blames your housekeeping for an infestation that clearly comes from the building, that is worth questioning — and a free review can help you understand who is actually responsible.
This is general information about California tenant rights, not legal advice. Every situation is different.