In my experience, it's a combination of a couple of things. First off, the field is heavily regulated (in the US anyway) and the penalties for violating regulations like HIPAA are incredibly high. Second, the field is currently dominated by major players such as Epic, so its pretty important to be compatible with them, but they don't really have an incentive to open up their ecosystem since they have such a stranglehold on the market. Finally, a lot of medical folks have been burned by technology in the past, and, in my experience, often view a lot of the tech they have to use as an insurance and government mandated evil, rather than a way to make their lives better.

Not to say things can't be improved, but there are a lot of factors that make it more difficult than a traditional B2B or B2C product.