Recruiting is pretty hard, actually. It takes a lot of moving pieces, and there's a lot of work to be done. This work is split between recruiters who manage the overall candidate relationship, interviewers who assess the candidates, and managers who are staffing their teams and thus do a lot of other work. There are also coordinators and all kinds of other folks.
If my understanding about product development is correct, it's not that different from building a product. Besides engineers, there are product managers, designers, researchers, and managers in that process as well. There are all kinds of processes and dependencies that go into it. Same with recruiting :)
Ultimately, I believe the heads of both Talent and Engineering have other responsibilities besides recruiting as well. Recruiting happens to be one where they share a lot of responsibility.