The default advice mode for processing @Transactional annotations is proxy, which allows for interception of calls through the proxy only. Local calls within the same class cannot get intercepted that way. For a more advanced mode of interception, consider switching to aspectj mode in combination with compile-time or load-time weaving.
Taken from Spring reference. https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/data-access.html#tx-propagation-nested