Telemedicine is still health care; health care is highly regulated, and regulations and licensing vary on a country-by-country and state-by-state basis (and perhaps to more local levels, as well). A doctor licensed to practice in, say, the UK, can't practice medicine in the US without getting a license to do so.
Some of the restrictions may be bypassed in the future by legislation that accounts for the potential of long-distance care, but on the other hand there may be significant safety concerns that are good reason to maintain the status quo.
I'm not sure what the best sources are to explain this, so I'll just quote Wikipedia:
Restrictive licensure laws in the United States require a practitioner to obtain a full license to deliver telemedicine care across state lines. Typically, states with restrictive licensure laws also have several exceptions (varying from state to state) that may release an out-of-state practitioner from the additional burden of obtaining such a license. A number of states require practitioners who seek compensation to frequently deliver interstate care to acquire a full license.
More specific and widely reaching laws, legislations and regulations will have to evolve with the technology. They will have to be fully agreed upon, for example, will all clinicians need full licensing in every community they provide telehealth services too, or could there be a limited use telehealth licence? Would the limited use licence cover all potential telehealth interventions, or only some? Who would be responsible if an emergency was occurring and the practitioner could not provide immediate help – would someone else have to be in the room with the patient at all consult times? Which state, city or country would the law apply in when a breach or malpractice occurred? 
A major legal action prompt in telehealth thus far has been issues surrounding online prescribing and whether an appropriate clinician-patient relationship can be established online to make prescribing safe, making this an area that requires particular scrutiny. It may be required that the practitioner and patient involved must meet in person at least once before online prescribing can occur, or that at least a live-video conference must occur, not just impersonal questionnaires or surveys to determine need.