Because other countries (European ones) have strict rules when it comes to health. They would not be so dumb to let an Apple watch dictate a persons health. but hay in the USA anything goes....
Well... It is not that simple. It is very difficult to compare the "strictness" of FDA and EU legislation.
In this case AW4 has the FDA clearance (not approval) so that it can be marketed in the US. In the EU it seems to fall into MDD (Medical Devices Directive) domain, which then sets another set of requirements. The requirements for MDD compliance might be stricter than those for FDA clearance, but when comparing MDD compliance and FDA approval, the latter is usually more difficult to achieve. Or at least that is what most players on the field think.
This is further complicated by the fact that the EU is right at the moment transitioning from MDD to MDR (Medical Devices Regulation), which is much more comprehensive, and in most cases stricter than MDD.
I know something about MDD, MDR, and FDA in practice, and personal smart devices such as AW4 are far from simple from the regulatory perspective. If you have a simple hardware (and fixed firmware) based medical device, the regulatory situation is straightforward. Just read the regulations and carry out all tests mandated by the regulation. After you have gathered that truckload of paperwork, someone will stamp it, and that's it.
But in AW4 you have a smart device which does a lot more than a medical device. It has some medical-device-related hardware and software running in it, as well as an app running in another device. What exactly is the medical device here? If the complete system (AW4 HW + WatchOS + iOS + app) is the medical device, it will never become MDR compliant. This is just because then all SW and HW in AW4 should comply to the relevant requirements, which is just impossible.
So, the regulators in any country need to decide which part of AW4 (plus the app) is "a medical device". Before that happens, the device will not receive any medical device approvals practically anywhere. The FDA is playing an important role here, and I guess there is a lot of international cooperation going on behind the scenes.
One possibility is to find out other arrangements similar to the FDA clearance. The device itself is not a medical device, but it can be used in personal use. This is probably the best route to take as these devices gain popularity. One trick that has been used is to label devices as "wellbeing" stuff—as has been done with HRM monitors in general. ECG, however, is so deep in the field of medicine that this explanation may not pass any serious scrutiny.
I am afraid the ECG functionality may not be available in the EU any time soon. The EU might still be the second one (or third after China) to get the ECG functionality, as the amount of money spent with specialists, lawyers, and regulatory agencies is approximately constant and independent of the market size.
