You're very observant. A recent study showed that the patients most likely to get a splint for tennis elbow are women with moderate to severe lateral epicondylitis. Lateral refers to the outside of the elbow. Epicondylitis is the medical word for tennis elbow.
It's not clear if this is because women have more pain than men or are more likely to have lateral epicondylitis. Perhaps there's some other factor involved. More study is needed to sort these things out.
It may not matter since several new studies have shown that splinting actually keeps a patient from recovering sooner. Patients wearing splints have more time off work and a longer recovery. They also have higher medical costs. It seems elbow pain (like back pain) gets better faster with movement and activity.