It is a fair question, and the answer comes down to responsibility and reality. The attacker is responsible for the crime, and the criminal justice system addresses that. But a property owner who ignored a known danger and failed to provide reasonable security may share responsibility for allowing the crime to happen — and that is what a civil claim addresses.
There is also a practical reason. An individual attacker often has no ability to compensate you for what you have been through, and a criminal case does not provide for your medical bills, therapy, or lost income. A property owner, by contrast, typically carries insurance — which is often the realistic source of the support you need to recover.
A civil claim against the owner is separate from any criminal case and does not depend on charges or a conviction. Holding a negligent owner accountable is both about justice — the harm was preventable — and about the practical support that helps you move forward.