afterCommit called before the whole transaction is finished

Question

I have this situation

@Component
@Slf4j
public class MainClass {

    @Autowired
    private SomeService service;

    @Autowired
    private OtherService otherService;

    @Transactional
    private Object save() {
        List<Object> objects = processSomething();
        return otherService.save(objects);
    }

    private List<Object> processSomething() {
        return service.doSomething();
    }
}

@Service
@Transactional
@Slf4j
public class SomeService {

    @Autowired
    private SomeService service;

    public Object doSomething() {
        List<Object> objects = List.of(new Object());
        doSomethingAfterCommit();
        return objects;
    }

    private void doSomethingAfterCommit() {
        if (!TransactionSynchronizationManager.isActualTransactionActive()) return;

        TransactionSynchronizationManager.registerSynchronization(new TransactionSynchronizationAdapter() {
            @Override
            public void afterCommit() { // triggered before otherService.save() call
                // some db operations to find records saved in otherService.save()
            }
        });
    }
}

@Service
@Transactional
@Slf4j
public class OtherService {

    public Object save(List<Object> objects) {
        // db operations to save all entities and returns one
    }
}

I'm confused as to why the afterCommit in doSomethingAfterCommit is being called before the save method of OtherService can even start. With how I set the Transactional annotations I thought all db operations would all be part of the same transaction, so the afterCommit would be called at the end of MainClass.save(). Why isn't it happening?