As I understand it, Healthcare.gov is simply an exchange presenting insurance plans that you qualify for based on your personal situation and location. Given that 25 states (or more) refused to create their own exchanges, the federal government became responsible for creating all of them, in one application. That's 25 exchanges each with multiple insurance providers, all of which likely have their own unique interface requirements, meaning that they need to receive information from Healthcare.gov in a format they can use, or can at least re-format, to work in their own enterprise architecture. I don't know how many insurance providers there are from each of the states included in Healthcare.gov, but imagine if 25 states had 10 insurance companies each...that's at least 250 different interfaces that are needed to just communicate with these insurance companies.
To re-purpose ST's waitress analogy...it seems to me that Healthcare.gov is less like a waitress in one restaurant and more like a delivery driver for one of 250+ restaurants. If the driver delivers the wrong (or no) order, good luck getting that straightened out.
My guess is that the problems Healthcare.gov are experiencing are every bit as much problems for the insurance companies represented on the exchange as they are for the website itself.