So you ought to say "The government should of just built healthcare.gov..." ... except that's very clearly not the style of this government.
E.g. one simple way to take traffic off most of the system would be to provide an interface to the subsidy calculation to entities beyond the state exchanges (who have to use it; when Verzion accidentally took the site offline, they couldn't do much), like insurers. It's said to be on the todo list, but at a very low priority.
http://www.independent.co.uk/life-style/health-and-families/...
Still, it's an epic failure, said to be the greatest single one in government IT contracting.
(E.g. I'll bet the FAA's eternal quest to upgrade from their 1940's (sic) technique and '60s or so architecture has cost more over time, but not any single failed effort.)
Also note that the NHS system was about building a database for every NHS health record across the country; prescription notices, medial history, etc. etc.
I'm not sure it'll even be legal now. HealthCare.gov isn't going nearly as far as that.
Even though I'm a Brit, some governments are making moves to modernise and open up their data for others to play with, over here we've got a great government-funded team working on exactly that (called the GDS). (http://digital.cabinetoffice.gov.uk/)
Frankly I think this is a massively expensive and missed opportunity for the US Government's digital service team.