Why availability of ECG is not universal, which can be used in any countries.

I bought Apple watch since Series 1 and continue buying a new release until Series 4. I bought series 4 because of ECG function. However, until this day ECG still not available in my country, Thailand. I would like to know why it is available in some countries and not in other countries. I don't know why Apple did not release it as international availability, as I think Apple Watch ECG is not certified as medical device (If so, then it is understood that certification for each country is needed). I think ECG function is similar to heart monitor function as it is vital sign monitoring, but only heart rate monitoring is internationally available when Apple Watch is released. I decided not to buy newer version of Apple Watch until ECG function is available, at least in Thailand, period!