In the US, to become a lawyer, you must go to law school and learn (all) types of law, since to become a lawyer, then to pass the bar exam is on (all) types of law.
This is becoming more common in all types of law practices. Many of personal injury lawyers are now taking on Social Security or WC clients, since there is so much competition out there, thus to keep the practice afloat, they need to expand to get/keep more clients.
My (late) husband practiced law for over 45 years. He handled all types of law, but in the last 10 years, he focused on what he did best, which was Social Security Disability. He was tired of family law, or criminal etc, since he wanted to retire and be able to close out his practice.